birthstones

May 8th, 2016

Somewhat like the Zodiac, certain gems are associated with each month of the year, called birthstones. Using or wearing each type of stone monthly was said to increase your luck or health for that month. Their use dates back to ancient times, when they were mostly identified by color rather than name. Birthstones are popular gifts in jewelry for loved ones, as they have a more personal significance to the owner than any regular gemstone.

The list and allocation of birthstones has not changed in over a century. Some months may have two or three stones to represent it, but there is often one gemstone that is the most commonly known as the symbolic birthstone. Note that the associated zodiac signs refer to the gemstone and not the month, and do not line up perfectly with the calendar. For example, Aquamarine is March’s birthstone, and Aries is March’s zodiac sign, but nevertheless, Aquamarine is commonly used as Scorpio’s gemstone instead.

BIRTHSTONES BY MONTH

birthstones

All of the birthstones by month.

JANUARY – GARNET

Associated zodiac sign: Aquarius | Other common January birthstones: Rose quartz

Although it can be found in a variety of colors, garnet is most popularly a deep red. It is said to prevent accidents and nightmares, and contains qualities of strength, prosperity and health. They are durable stones, without cleavage, slightly transparent, and somewhat more common than the others on this list.

FEBRUARY – AMETHYST

Associated zodiac sign: Pisces | Other common February birthstones: Onyx

Amethyst is essentially a purple version of quartz. In ancient times, it was the prevention for drunkenness, and it is associated with sobriety, spirituality, wisdom, and security. Amethysts are widely available and come in a large variety of shapes and sizes.

MARCH – AQUAMARINE

Associated zodiac sign: Scorpio | Other common March birthstones: Bloodstone

Aquamarine is a blue-green variety of beryl. It is slightly transparent with a hard and cylindrical nature. It embodies eternal life and is said to be healthy for married couples. Youth, beauty, honesty, loyalty, and happiness are its associated values.

APRIL – DIAMOND

Associated zodiac sign: Aries | Other common April birthstones: Quartz

April babies get the privilege of having diamond, the highly treasured gemstone, as their birthstone. They are the hardest mineral of all at a Moh’s rating of 10, and have been used as gemstones for wedding rings as a tradition for hundreds of years. The ultimate gift of love, diamonds are highly reflective gems associated with invincibility, clarity, and purity.

MAY – EMERALD

Associated zodiac sign: Cancer | Other common May birthstones: Chrysoprase

The lovely deep green emerald gemstone is the mineral emblem for people born in May. They symbolize fertility, patience, understanding, and rebirth. Ancient Egypt’s Cleopatra was famous for wearing emeralds. Emeralds increase in rarity and value the deeper and richer the green color is.

JUNE – PEARL

Associated zodiac sign: Cancer | Other common June birthstones: Moonstone, alexandrite

Pearls are somewhat of the odd one out when it comes to birthstones. They are the only ones that have less of a refractive surface and instead have a pearly and opaque appearance. They cannot be carved into elaborate shapes, but must remain spherical. They are formed from mollusks under the sea and are not purely gemstones, formed from minerals along with a structural protein called nacre. They symbolize modesty, purity, and beauty.

JULY – RUBY

Associated zodiac sign: Capricorn | Other common July birthstones: Carnelian

Rubies are the lighter red cousin to Garnets. A variant of the mineral Corundum, they are fairly hard at a Moh’s scale of 9 and often very reflective. They symbolize love, success, passion, promise, and good fortune. They were often valued by kings and people in power.

AUGUST – PERIDOT

Associated zodiac sign: Libra | Other common August birthstones: Sardonyx

Peridots are an elegant, distinctive lime green color and can be used to bring healing properties to the wearer. They are also known under the name of olivine. This transparent gemstone shot to popularity when a peridot-rich deposit was discovered in Pakistan. Fame, dignity, and protection are some of the values connected to peridot.

SEPTEMBER – SAPPHIRE

Associated zodiac sign: Taurus | Other common September birthstones: Lapis lazuli

Truth, sincerity, and commitment are commonly associated with this beautiful mineral, another derivative of corundum. Sapphires are mostly known in their deep blue variant, but they can also be yellow, pink, orange, peach, and other colors. Their ties to the value of trust makes them popular engagement stones. Salmon-colored sapphires, known as Padparadscha, are some of the most highly valued gems in the world.

OCTOBER – OPAL

Associated zodiac sign: Scorpio | Other common October birthstones: Tourmaline

October children are represented by the gemstone opal. Beautifully radiant, opals are referred to as the “Queen of Gems” due to containing the colors of all the other gemstones. This is due to containing tiny spheres of minerals that refract light and create a multitude of colors. They are affiliated with hope, faith, and confidence.

NOVEMBER – TOPAZ

Associated zodiac sign: Scorpio | Other common November birthstones: Citrine

Topaz is famous for its golden-brown or orange hue, but can also be green, blue, pink, yellow, colorless, or other colors. They are common confused with citrine, which shares many of the same properties. It has a Moh’s rating of 8 and has a wonderful luster. Topaz represents strength, wisdom and courage.

DECEMBER – TURQUOISE

Associated zodiac sign: Sagittarius | Other common December birthstones: Tanzanite, zircon

Turquoise, as the name indicates, is a blue, opaque gemstone. It was valued by Native Americans and Persians. Crystals are very rare and usually small, making them expensive on the jewelry market. New opportunities and happiness are affiliated with turquoise.

Which birthstone is yours? Remember these in the future as ideas for a gift for a loved one or yourself.

Advertisements

focused study: granite

May 8th, 2016

If you’ve ever remodeled your kitchen, walked the floors of a hotel or museum, or even just taken a walk by your local river, chances are you’ve seen your fair share of granite. It is one of the most common rocks and is used for many practical purposes. Its durability and easy-to-handle nature combined with its aesthetic appeal and commonality makes it one of the most desirable stones for floors and walls. It is not necessarily the prized possession of an avid rock collector, but nevertheless, it is a useful addition.

rock-landscaping-transitional-landscaping-rocks-in-el-paso-tx-landscaping-rocks-san-antonio-landscaping-rocks-salt-lake-city-landscaping-rocks-sunshine-coast-landscaping-rocks-sydney-landscaping

Due to its crystalline appearance, granite is often dubbed the “salt and pepper” rock.

FORMATION

Granite is a highly variable rock, causing a number of formation theories to be explored. Its basic definition as an intrusive igneous rock means that it originates from the hardening of molten material underneath the Earth’s surface, but beyond that, the material that it is made out of is debatable. Each granite is unique, and we can point to its mineral makeup to discover what molten rock it was made from. For example, granites comprised mostly of alkali feldspar may originate from melted sediments. Minerals in granite crystallize at different rates, causing higher concentrations of silicon, aluminum, and potassium. 

A second process, called granitization, may also occur. A chemically similar rock may undergo intense metamorphism, creating a new rock without undergoing a state change. In addition, rocks must be in an area with a lot of water, as water helps these processes occur by transporting sediments through vapor. Some geologists doubt this theory as the combination of heat and pressure along with the abundance of water is not a likely scenario.

PROPERTIES

Type of rock: Igneous

Contained minerals: Feldspar, quartz, k-feldspar, mica

Color: Usually white, red-orange, beige, or gray, with dark black flecks and crystals (but can vary)

Luster: Vitreous (can vary depending on contained minerals)

Cleavage: Poor

Fracture: Since granite is not a mineral, it does not have an identifiable fracture (the fracture of minerals contained in granite vary too greatly to consolidate)

Hardness: Moh’s scale 6-7 (about equivalent or slightly harder than a steel nail)

Transparency: Opaque

Streak: Colorless or white

Texture: Phaneritic

TYPES OF GRANITE

Again, granites are highly variable. They are usually identified by their primary color and the location where they are found. Depending on where they are in the world and what minerals they contain, many of them appear different from each other, but they are all granites nonetheless.

Bianco Romano: Attractive white granite with sparse brown flecks and streaks.

Absolute Black: Nearly pitch-black variation with very few, if any, flecks of white.

Tumkur Porphyry: Mottled red and black granite with large blotches of color. Some light gray streaks. Found in India.

Sapphire Brown: Black granite with woodchip-shaped tan blotches and white marbling.

Tropical Green: Elegant green granite with streaks of red and white.

Click here for a full list of types of granite.

LOCATION

Granite can be found all over the world, and perusers of granite take pride in their unique local variations. It is usually underneath other layers of sedimentary rock in mountain ranges. It can also be found in “batholiths”, or huge cliffs of stone. There are not many special conditions that make granite unique to one area of the world, so they are one of the most common neighborhood rocks. The commercialization of granite has also lead to its spread through transportation.

FUN FACT

Although granite is one of the most well-known rocks, it is commonly misidentified in commercial use. Any rock with a coarse grain can be mistakenly called granite, the biggest offenders being gneiss and schist. The main reason for this is to avoid customers being turned off by the title of a “schistic” countertop. Granite is seen as a somewhat attractive term for home designers.

Additionally, curling rocks are traditionally made of polished granite.

magic rocks

May 8th, 2016

This short clip shows how easy it is to be fooled by the superstition of “magic rocks” into making an unnecessary purchase.

Whether you believe in them or not, rocks are a symbol of balance, peace, earth, and healing for many. The natural appeal and beauty of rocks and minerals have made them a magical staple for everything from massages to fortune telling. Each type of rock is thought to have its own individual synergy and can be used to help believers through a variety of problems. Rocks are even processed and polished differently to bring out their magical potential.

Here’s how you can get started to better your connection to the earth:

THE 7 CHAKRAS

e233ebf2-b537-4619-a8d2-3b1f4b468144_560_420

Placement of the 7 chakras.

Chakras, meaning “wheels” in Sanskrit, are the representations of the energies of the body. There are 7 chakras, each focusing on one part of the physical body. They are also associated by corresponding colors, starting with red at the base and working up in rainbow order to purple at the head. The goal of people who use magic crystals is to vitalize and balance their chakras and restore their body to perfect condition.

FIRST: ROOT CHAKRA

Color: Red or Black | Location: Base of spine | Element: Earth

The root chakra represents your connection to the Earth, and is associated with grounding, stability, balance, and security. It also embodies your basic need for survival.

Without a strengthened root chakra, you may feel anxious or insecure. Problems with appetite and sexual frustration in men may occur.

Gems for Root Chakra: Bloodstone, obsidian, garnet, smoky quartz, hematite, black tourmaline

SECOND: SACRAL CHAKRA

Color: Orange | Location: Stomach | Element: Water

The sacral chakra represents creativity, sexuality, desire, emotion, and intuition. It is important to have this chakra centered to fully indulge in natural pleasures and processes. This chakra also improves your confidence and friendliness, as well as your ability to socialize and relate.

A blocked sacral chakra leads to emotional instability, manipulative thoughts or feelings, or lack of energy. Physically, issues with the kidney or liver or a stiff lower back can occur. Females may feel sexually frustrated.

Gems for Sacral Chakra: Carnelian, citrine, orange calcite, tiger’s eye

THIRD: SOLAR PLEXUS CHAKRA

Color: Yellow | Location: Centered below the breastbone, above the navel | Element: Fire

The solar plexus chakra represents personal power, ego, ambition, anger and impulse control, and healthy metabolism. A balanced solar plexus chakra improves your cheerfulness, risk-taking abilities, and ability to value yourself.

An uncentered solar plexus chakra leads to loss of confidence, low mood, confusion, and worries about how you come off to others. Diabetes, digestive problems, and allergies are examples of physical issues.

Gems for Solar Plexus Chakra: Amber, citrine, golden calcite, topaz, aragonite, yellow sapphire

FOURTH: HEART CHAKRA

Color: Green | Location: Center of chest | Element: Air

The heart chakra represents love, compassion, and spirituality. Empathy and connection to the spirit are also associated with the heart chakra.

A blocked heart chakra leads to paranoia, fears of getting hurt, indecisiveness and feelings that you are unworthy of being loved. Heart attack, troubles breathing, high blood pressure, and insomnia are symptoms of this.

Gems for Heart Chakra: Moonstone, tourmaline, emerald, green calcite, aventurine, malachite, peridot, rose quartz

FIFTH: THROAT CHAKRA

Color: Blue | Location: Throat | Element: Sound

The throat chakra represents your communication center, sound, and expression of creativity. It minimizes self-consciousness.

A blocked throat chakra leads to shyness, inability to express thoughts, quietness, and weakness. You may get a sore throat, ear infection, skin inflammations, or back pain.

Gems for Throat Chakra: Sapphire, aquamarine, quartz, blue lace agate, angelite, blue calcite

SIXTH: THIRD EYE CHAKRA

Color: Indigo | Location: Forehead | Element: Light

The third eye chakra represents your visionary process, psychic intuition, spiritual guidance, and sense of understanding. You may feel more aware or insightful when this chakra is balanced.

Without balancing your third eye chakra, you can feel egotistical, or conversely, non-assertive. Physical ailments include blindness, blurred vision, and headaches.

Gems for Third Eye Chakra: Diamond, amethyst, lapis lazuli, sodalite

SEVENTH: THE CROWN CHAKRA

Color: Purple or White | Location: Top of head | Element: Thought

The crown chakra represents spiritual thought, enlightenment, and consciousness. Connection to God is fostered through this chakra. The string connecting all of your seven chakras begins from this point. It is also where the soul enters the body at birth, and leaves at death.

With a blocked crown chakra, frustration, depression, and loss of joy may occur. You could also experience migraines.

Gems for the Crown Chakra: Amethyst, white calcite, white topaz, sapphire, quartz

HOW TO USE YOUR CRYSTALS

Now that you’ve figured out which crystals you need to balance your energies, how do you connect with them? There are a multitude of methods you can use your crystal with to maximize its potential. Here are a few:

Under your pillow: As you sleep, the crystal can protect you from insomnia or nightmares. As your body is most relaxed while sleeping, it is a good way to connect with your central energies.

Gem essences: By soaking a (safe, non-toxic) gem or crystal in a bath of water overnight, you can let the energies of the crystal dissolve in the water. You can then drink the essence, wash yourself with it, or use it as a spray around your home.

In meditation: Holding a crystal or placing one in front of you can better your concentration and help you relax.

While bathing: Use your crystals in the bath by placing them around or in the water. This will absorb any negative energy you have pent up.

Simply placing them anywhere: Even the mere presence of a healing stone can positively change the energy of a room. At work or at home, display your crystals in a room and be reminded of their cosmic power when you enter it.

rock art

May 2nd, 2016

Rocks have existed for millions and millions of years, preceding life and modern human culture as we know it. And because they can change so slowly over time, they are fantastic preservers of prehistory. For example, take fossils. Nearly 521 million years ago, trilobites, one of the earliest known arthropod species, left behind their skeletons to be preserved in overlapping layers of rock and discovered later. And yet, scientists were able to discover entire fossils of trilobites and piece together what they would be like back then due to it. That’s why rocks must be considered one of our most valuable resources for preserving history.

cambrian_trilobite_olenoides_mt-_stephen

Trilobite fossil, magnified.

Although fossils are interesting, as the skeletal structures are more interesting than the rock itself, I won’t go into detail about them here. The purpose of this entry was to focus on rocks being actually defaced and used as a canvas – prehistoric rock paintings and etchings. Before the invention of paper, rocks and tools were the primary way of making your mark on society. And they have held up well.

Two main terms are used to categorize prehistoric rock art.

PETROGLYPHS

large-cup-marks20or20cupules20at20peja

Cupules in Islamabad, Pakistan.

Petroglyphs refer to when pieces of rock are actually carved away to create unnatural impressions in the rock surface. The markings usually have cultural significance rather than functional significance, and are used for decoration. Such is the case with cupules, the most famous type of petroglyphs, found on every continent sans Antarctica. These mysterious bowl-shaped engravings seemed to be the most popular form of primitive art during the Middle or even Lower Paleolithic periods (up to 2.5 million years ago). They tend to be associated with the Stone Age as our ancestors were just beginning to practice using more advanced tools. Although the purpose of cupules remains a mystery as reasons could vary from location to location, studies in Africa show that it served a ceremonial purpose. Witnesses to modern cupule-makers reported that according to the artists, mineral dust released from hammering into the rock was believed to increase fertility and thus food supply in female cockatoos. Whether the rocks served a similar purpose before modern culture evolved is unknown, making the cupules a prominent yet mysterious landmark.

PICTOGRAPHS

1024px-newspaper_rock_is_a_large_cliff_mural_of_ancient_indian_petroglyphs_and_pictographs_remarkable_for_the_clarity_of-_-_nara_-_545671

Ancient Indian pictographs.

On the other end of the spectrum, pictographs refer to when pigment is applied onto the face of the rock. The preferred mediums: urine, blood, charcoal, berry juice, crushed bone, anything that would stain. The preferred tools: fingers, small styluses, animal hair brushes, anything that you could control. Although pictographs are far less durable due to weathering and erosion, ancient paintings dating back to 17,000 BCE can still be found in caves sheltered from harsh winds and water. Common themes included basic scenes of hunting, and animals appeared more often than humans. These older images may have been used to communicate as one of the earliest forms of writing. They later involved into the technique of ideograms – pictures that convey ideas – and recurring symbols adapted over time to create a more consistent way of expressing words.

My own rock painting experience was special in a different kind of way. When I was in preschool, my class sat down with a batch of plain gray pebbles and white paint, and we all drew careful lines around the perimeter of the rocks. They were called “wishing rocks”, which you could skip across the water and wish upon, similar to wishing on a shooting star. The line must be unbroken and clear to grant your wish.

Of course, this only amounted to a painting practice activity rather than a serious superstition, but it can be compared to other forms of rock art around the world. A rock with little functional purpose, believed to have metaphysical properties, defaced to appeal to the beliefs of the artist. Rocks are not just unmoving natural structures, but important cultural symbols that constantly interact with human life, whether it be pebbles painted with white in a sunny preschool classroom or cliffs stained with animal blood in history.

Although etchings in rocks are much more of a rare, specialized process now, rocks are still one of the best ways to freeze an era in time forever. They were our first permanent canvases from which cuneiform and religious beliefs were born.  And contemporary forms of pictograms are used everywhere – road signs, bathroom labels, commercial logos. Rocks tend to take somewhat of a backseat when historians delve into prehistory, but in reality, they are the foundation on which modern culture was built up.

focused study: meteorites

April 30th, 2016

Rocks and minerals are not specific to just our planet. Millions of miles away, rocks can be found in the crust of planets, asteroids and meteoroids in the vast sea of space. Although we have been able to extract rock directly from the moon due to modern astronomy, most of our encounters with space rocks occur when a meteor, a small chunk of rock, hits our earth.

When we see a shooting star, that is a telltale sign that a meteor has entered Earth’s atmosphere and is launching towards our surface at 18 miles per second. Most meteors disintegrate due to the high pressure and heat of the Earth’s atmosphere, and very few actually make impact with the surface. When they do, however, the effects can be terrifying.

meteor_crater_near_winslow_arizona

Meteor crater in Arizona, the biggest preserved to date.

Meteors are actually much more common than we think. Millions of them enter our atmosphere each day, although these are commonly around the size of a grain of sand, and we tend to think they are a rare occurrence because we can usually only see them at night and when they are big enough. Meteors are hardly anything to worry about, although the idea of the debris of space colliding with our planet’s atmosphere is pretty interesting and has been a hot button topic among geologists and astronomers alike.

This is where the focus reverts back to rocks. When meteors burn, very rarely they can leave behind chunks of iron or rock, called meteorites. These specimens can be crucial to studying the conditions of outer space, as their formation can differ from Earth due to the huge variety of temperatures and effects of gravity.

Meteors are almost considered sacred among many communities and are often believed to have metaphysical healing properties, like other rocks. Their mysterious and alluring aura make them special among collectors and researchers.

Unfortunately, I do not have a meteorite of my own, but space being one of my favorite topics to study in science other than geology, this marriage of my hobbies seemed like a perfect blog entry to write.

COLORS

When meteors burn, they can shed a variety of different colors to an onlooker. This shows which minerals the meteor was composed of.

Orange-yellow – sodium

Yellow – iron

Blue-green – magnesium

Violet – calcium

Red – oxygen and nitrogen

TYPES OF METEORITES

Meteorites are categorized by their composition, as they are often made up of rocky material, iron, or a combination of the two. Meteorites can be formed by the same recognizable igneous processes as we have on Earth, but as they live under different conditions and come from a variety of extraterrestrial bodies, they also undergo different processes that make them unique.

IRON-NICKEL METEORITES

These meteorites are comprised heavily of iron and nickel and do not usually contain much silicate material (therefore, they cannot be considered rocks). They are identified by their heavy weight and cross-hatched, silver texture when cut. Their “fusion crust”, or the remnants of their crusty surface after heat from the atmosphere melted the majority of it away, is usually brown. They were a prime source of metal in ancient times.

Screen Shot 2016-04-30 at 10.38.39 PM

The cross-hatched structure of an iron-nickel meteorite.

PALLASITE METEORITES

A mixture between silicate material and iron (making them half-rocks), pallasites contain pockets of olivine (commonly named peridot in the gemstone world). They are possibly of volcanic origin and share qualities with igneous rocks.

SONY DSC

A beautiful example of a pallasite. The small, golden flecks are bits of the mineral olivine.

CHONDRITE METEORITES

The most common form of meteorite, mostly made of silicate, with flecks of metallic material (so… now they are rocks). Chondrite meteorites are composed of molten egg-shaped grains called chondrules, buried in a larger, soft gray rock similar to graphite.

6chondrite3301

A chondrite meteorite, with the fusion crust still visible.

PROPERTIES

The exact properties of a meteorite can vary, although they share some characteristics.

Color: Commonly dark gray or black when first fallen due to a “fusion crust”. As a meteorite spends more time on Earth, the crust withers away and the meteorite turns a dull brown.

Weight: Many remark that it is much heavier than the average rock due to the high pure iron content.

Fracture: Jagged and irregular, hackly.

Texture: Meteorites are usually somewhat smooth, although they can contain thumbprint-like impressions called regmaglypts, caused by the meteorite being exposed to hot gas and burning off surface layers while shooting down to Earth.

In addition, stony meteorites can have small, grain-like bits of metal in their interior holding them together. Some even contain precious gemstones such as olivine.

METAPHYSICAL PROPERTIES

Meteorites are believed to have an odd energy associated with them due to their connection to space, and can enhance the abilities of telepathy and inter-dimensional communication. Magnetic types of meteorites can be used to ground someone and repel bad energies, and are a symbol of meditation, patience and balance. They are also believed to heal by strengthening the blood and tissue. Meteorites are symbols of endurance against long-term struggles due to the way they fall to Earth.

properties of rocks and minerals

April 30th, 2016

Rocks and minerals come in all shapes and sizes, and just like people, they are sometimes categorized by how they look and where they come from. Geologists have devised many tests that can be performed on rocks in order to better understand their properties. These can also be vital in identifying unknown specimens, like I attempted to do during this project.

COLOR

Most rocks and minerals have a range of colors that they can appear in due to the traces of chemicals in their composition. Color is usually described through basic terminology and not complex colors (i.e. reddish-brown, not rust), whose definitions can vary from person to person. Although color is what most people identify first when examining a rock, it cannot be relied on alone to identify the specimen.

HARDNESS

Frederich Mohs, a German mineralogist, devised the Mohs scale as a measure for determining the hardness of rocks and minerals in 1812. The scale varies from 1 to 10, with specific rocks at each hardness. The general rule is that a rock with higher Mohs hardness will always scratch a rock that is softer. Other objects, such as a steel file or porcelain, can be used to perform tests on a rock sample and determine its hardness if someone does not have the full range of rocks available.

1 – Talc

2 – Gypsum (Roughly the hardness of a fingernail)

3 – Calcite (Gold has a hardness of 2.5-3)

4 – Fluorite

5 – Apatite

6 – Orthoclase Feldspar (A steel file has a hardness of 6.5)

7 – Quartz (Porcelain also has a hardness of 7)

8 – Topaz

9 – Corundum

10 – Diamond

LUSTER

Minerals, depending on how they are formed, can reflect light differently. The “luster” of a mineral refers to how shiny or dull a mineral is.

Metallic – strong reflection similar to metal or iron

Vitreous – bright, like broken glass

Resinous – smooth and shiny, like resin or honey

Greasy – dull sheen, as if coated in oil

Pearly – reflective and iridescent, like pearl

Earthy – dull and toned down, similar to unglazed pottery

Silky – light reflects off of fibers, like silk

Adamantine – brilliant, like diamond

Waxy – like the surface of a candle

TRANSPARENCY

Transparency refers to a mineral’s ability to filter light through it. Opaque means no light can pass through the mineral, and no image can be seen through it. Translucent means that some light can pass through the mineral, allowing a vague image of an object on the other side. Transparent means that light can completely pass through a mineral, letting a viewer see an object clearly through it.

CLEAVAGE

Some minerals can be broken evenly across parallel planar surfaces, similar to how paper can be cut along a “grain”. Cleavage can be categorized as perfect (the break is even and clear planes are established), imperfect (the mineral has cleavage, but the planes are uneven and rough), or poor (planes are very difficult to distinguish). Some minerals do not experience any cleavage.

FRACTURE

Minerals that do not have cleavage have a balanced and strong atomic structure that is not weaker in any direction. Minerals carrying this characteristic have fracture. Fracture can be categorized as conchoidal (a smooth break, curved like a bowl), hackly (sharp and jagged), uneven (rough and irregular), or fibrous (breaks along distinct fibers, splinters like wood).

STREAK

When rocks are examined as large chunks, small minerals hidden in their composition can change how light reflects off of them and alter the color. For this reason, streak, or the “true color” of a rock or mineral, is a more accurate measure for identifying a sample. Streak is tested by scratching a rock or mineral along a porcelain surface to extract a powdered form of the sample. The streak can be drastically different from the apparent color.

SPECIFIC GRAVITY

Specific gravity is the ratio of the mineral’s weight to an the weight of an equal volume of water. There are no specific and universal quantities that make a rock light or heavy – most of it is just relative to a geologist’s intuition. An “average” specific gravity, like that of quartz, is around 2.7.

CHEMICAL FORMULA

This property is specific to minerals. It refers to the chemical makeup of the mineral. For example, diamond is a form of hardened carbon, and has the chemical formula C.

GRAIN SIZE

This property is observed only in rocks, and refers to the size of the small crystal formations found in a bigger rock. It is usually used to determine if a rock is igneous, sedimentary or metamorphic. Grain sizes can be coarse (larger than 2 millimeters), medium (1-2 millimeters), or fine (less than a millimeter thick).

TEXTURE

This property is specific to igneous rocks. The texture is not the roughness of the surface of the rock, but rather the distribution and size of smaller mineral grains in the rock that can change the surface’s appearance.

PYROCLASTIC:

Small bits of ash and remnants of rocks are trapped in the igneous rock after the explosive eruption of a volcano.

PHANERITIC:

Large crystals are easily visible in phaneritic rocks due to slow crystallization. Granite is an example of this type of texture.

APHANITIC:

Contrasted to phaneritic rocks, aphanitic rocks cool quickly on the Earth’s surface and have very fine grains that cannot be seen without the aid of a microscope.

PORPHYRITIC:

Porphyritic rocks form when temperature conditions quickly change, suddenly stopping crystals from fully forming during their growth process due to rapid cooling. This causes a mix between fine and coarse grains.

GLASSY:

Extremely rapid cooling prevent glassy-textured rock like obsidian from forming crystals at all. The rock appears like glass and breaks conchoidally.

VESICULAR:

Gas bubbles create air pockets in this type of igneous rock when cooling occurs. This creates craters not filled with any type of crystal.

FROTHY:

Frothy-textured rocks appear bubbly and abrasive. This occurs because of rapid cooling of a gassy magma.

focused study: agates

April 27th, 2016

When I was little, my family would drive up to Lake Superior in northern Minnesota for summer vacation. We stayed in a cramped rental cabin that smelled of wet wood, and I was too scared to take the top bunk bed because it was too high up.

More than anything, though, I remember the lakefront. Thousands and thousands of unique pebbles in all types of colors and sizes would stretch on for as far as the eye could see, the gentle waves of the lake’s shore soaking the closest few feet. Taking my parents’ hands, we would pick our way down the shore on an adventure, always looking down at the uneven rocky floor to gain our footing.

IMG_0713

And every so often I would bend gently down and sift through the gravel until I found a rock that I liked. My dad found some really interesting ones that had bulging “eyes” – he gave them to me to look at. They were called agates, Lake Superior’s signature mineral. Some of them had more than two eyes, some had layers and layers of alternating brown and white, and sometimes the rings crashed together and overlapped, like ripples in the salty Superior waters.

Past that, my memory fails me, as it was a long time ago, and all of the days muddle together. But when I decided to do this project, and dug up the dusty Ziploc bags with our old Lake Superior rock and mineral collections from the gift-wrapping cabinet, agates were clearly the thing that we were focused on finding back then.

FORMATION

Agates form in small crevices in host rocks, left behind by an animal or obstruction. The host rock can be any type – metamorphic, igneous, or sedimentary. Impure water rich in minerals such as silica washes over these holes and over time leaves behind deposited minerals, which crystallize along the sides. As each agate begins to crystallize, different types of mineral water fill the cavity in again, leaving behind different types of minerals. This is what forms the “band” effect that is characteristic of most agates and causes different layers to be of varying opacities and colors. Agate differs from its cousin chalcedony in this way – it must have layers of alternating types of minerals. For this process to occur, there must be a delicate balance of natural elements including pressure, moisture, and density of the host rock to prevent it from collapsing in on itself while forming. This process takes millions and millions of years, making each agate unique and ancient.

PROPERTIES

Refer to this list to understand these properties.

Found In: Igneous, metamorphic and sedimentary rocks

Chemical Formula: SiO2

Color: Various (common types are white, orange, brown, red, or gray)

Luster: Waxy

Cleavage: None

Fracture: Conchoidal

Hardness: Moh’s scale 6.5-7 (about equivalent or slightly harder than a steel nail)

Transparency: Transparent to opaque depending on nature of deposits

Streak: White

Texture: Smooth

TYPES OF AGATES

Shown here in detail are only some of the more common types of American agate – others, such as those specific to other countries, can be seen near the bottom of the section.

FORTIFICATION AGATE:

When cut down the middle, this very common type of agate shows impressive layers radiating out from and fortifying a “center”.

WATER-LINE AGATE:

Gravity conditions allow these agates to form parallel layers stacked within the outer shell.

EYE AGATE:

These attractive agates are formed when chalcedony minerals are drained, leaving several droplets that begin to crystallize into “eyes” that are solid, circular blemishes on the agates’ surface.

GEODE AGATE:

An agate that was unable to finish filling up with minerals is called a geode agate. It is characterized by its hollow, hard, crystallized center with bands radiating out like a normal fortification agate.

MOSS AGATE:

Resembling a landscape of trees, moss agates are formed when other mineral inclusions such as Fe or MgO prevent chalcedony from filling the agate regularly.

OTHER TYPES OF AGATES:

Shadow Agate | Tube Agate | Plume Agate | Full List of Types

LOCATION

Lake Superior is the most famous location for finding your own agates on the shore in the US. Agates are found all over the world, including in Mexico, Germany, Brazil, and India.

FUN FACT

Agates, like many other rocks and minerals, are believed to hold metaphysical properties that can cure people of physical or mental ailments. Among those traits are beliefs that they can bring good fortune, relieve allergies, prevent insomnia, and even lend courage.

This is the first of a series of individual entries on rocks and minerals. When more entries are up, I will link them here.