Minerals

A mineral is a:


 * naturally occuring
 * inorganic
 * solid
 * with fixed chemical composition
 * and fixed crystal structure.

Quartz
Quartz is made of silica and oxygen.

See a color 3D models of quartz crystals here!


 * Quartz is usually totally transparent, with a glassy luster.
 * It often forms beautiful crystals, like in a geode.
 * It is hard to scratch and hard to dissolve, but it can break if you smash it.
 * The reason for this strength is the regular crystal structure within the mineral.
 * All the Silicon and Oxygen atoms are arranged in a fixed pattern in 3D space.
 * These atoms are joined by COVALENT bonds
 * You can break quartz if you hit it with a hammer, and the pieces will look like broken glass.
 * Quartz crystals can weather, erode, and transport down to the sea and build up on beaches and river beds, where they later form sand stone layers.

Where do we find quartz, and how does it get there?
Quartz forms naturally, without aid of life, in lots of places:


 * Quartz can grow into large beautiful crystals, like in a cave or inside a geode.
 * Check out a cool color digital model of a geode here!
 * If it has color, this is from little chemical impurities that cause light to bend through the crystal.
 * Quartz can get "gemstone" names for these colors: rose quartz, smokey quartz, amethyst, etc.
 * Check out a color digital model of amethyst here!
 * Quartz can form crystals within magma or lava.
 * lava rocks that cool right away can cause quartz to form without distinguishable crystals.
 * examples include obsidian and pumice
 * Magma that cools slower, under the earth's surface, can allow larger quartz crystals to form, so you can see them distinctly.
 * examples include granite, diorite, etc.
 * If the ingredients for quartz are dissolved in water with certain chemical properties, it can form
 * in cracks between other minerals or sand grains;
 * or by dissolving other minerals at their edges and re-solidifying these parts as quartz elsewhere;
 * or it can REPLACE whole seashells, creating glass-like fossils with super detailed shapes.

Quartz is one of the most fundamental ingredients in sedimentary rocks.
Sandy beaches in California, Oregon, and Washington include lots of quartz grains.

These grains were formed by:


 * weathering the original rock where the quartz formed (see above) - maybe a granite;
 * transporting the bits of quartz long distances, like via a river;
 * eroding the quartz by smacking pieces together for years as they shift along the riverbed;
 * further eroding the quartz by smacking it against other grains as they shift along the ocean beach.

Sand can make SANDSTONE in the right conditions. See Depositional Environments to learn more.

Mica
Mica is made of oxygen, silica, and lots of little cations, like calcium, potassium, etc.

Check out a color 3D model here!


 * Mica is usually a little bit transparent, with a shine and feel like nice new plastic.
 * One chemical form makes the sheets almost black, with a little bit of a metalic, bronze look.
 * The other chemical form makes the sheets almost clear, with a little bit of a yellow look like old bottles.
 * It forms as sheets stacked together.
 * Big sheets are rare to see in nature, but easy to buy at a store because they are sold commercially.
 * Usually we see mica sheets in nature as shiny little flakes in rocks or in sand.
 * It is easy to scratch and fairly easy to dissolve, and it will break if tossed around.
 * Each sheet is made of silica and oxygen with strong COVALENT bonds (like quartz),
 * but the sheets are held together with weak ionic bonds.
 * It's fairly easy for water to strip the ions out from between the sheets.
 * Mica can weather and erode into little flakes or dust as it travels with sediment and sand.
 * It's easy to see, like in beach sand or a sandstone rock, because of it's little glitter look.
 * It's easy to remove from a natural system by smashing and dissolving it entirely.

Where do we find mica, and how does it get there?
Mica forms naturally, without aid of life, in two main ways.


 * Mica can form crystals within magma.
 * Magma that cools slowly, under the earth's surface, can allow mica mineral sheets to form.
 * examples include granite, diorite, etc.
 * In these rocks, the mica are the bits that look most like glitter.
 * Mica also forms in metamorphic rocks.
 * If the parent rock has the right atoms, heat and pressure inside the Earth's crust can shift them into the mineral mica.
 * Examples include the metamorphic schist and gneiss (pronounced "nice").
 * These rocks are valuable as building materials because they are shimmery, a look that comes from the tiny mica sheets.

Mica is important in sedimentary rocks.
Sandy beaches in California, Oregon, and Washington include lots of quartz grains, and SOME of these beaches also have lots of tiny mica sheets.

These tiny mica sheets were formed by:


 * weathering the original rock where the mica formed (see above) - maybe an igneous granite or a metamorphic schist.
 * transporting the bits of mica long distances, like via a river, where they break into smaller sheets and flakes
 * further breaking the mica sheets as they shift along the ocean beach.

Mica can get destroyed by enough weathering and erosion!


 * "Mature" sand will have no mica, because it's been weathering and eroding for so long.
 * Sand with mica is "immature", because the mica hasn't been all destroyed yet.

Observing mica in sand, or in a sedimentary rock, helps a paleontologist interpret:


 * How long the sand was moving about;
 * How far the sand traveled;
 * Or how active the depositional environment was.
 * Mica flakes drift easily in water.
 * Mica flakes in a sandstone tell us the water was CALM enough to let the mica settle.
 * A LACK of mica flakes might mean the sediment was more mature, or the water was too active to let mica settle.

Sand can make SANDSTONE in the right conditions. See Depositional Environments to learn more.

Mica is also very common in cosmetics, particularly eye shadow, because:


 * It is shimmery.
 * It occurs naturally so it's cheap to gather and can be marketed as "all natural" or whatever.
 * Naturally-occurring dark mica is a good source of rich, dark color.
 * naturally-occurring light mica is easily dyed bright colors.
 * Mica doesn't soak into skin or react chemically with skin.

Feldspar
Feldspar is made of oxygen, silica, and lots of little cations, like calcium, potassium, etc.

Check out a color 3D model here!


 * Feldspar is opaque, with a greasy luster.
 * One chemical form is usually a dusky pink. The other is usually a dirty white.
 * It forms as trapezoid prisms - like cubes, but with a little bit of a lean.
 * You can find big chunks - the size of a golf ball or racketball - while hiking in the mountains.
 * Usually we see feldspar as the opaque bits of granite, as the opaque grains in sand, or as the dull and orange-y bits in sandstone.
 * Feldspar is hard to scratch and fairly hard to dissolve, and it will break if hit with a hammer.
 * Feldspar has a MIX of covalent and ionic bonds.
 * Dissolving or breaking feldspar is easier than quartz, but harder than mica.
 * Broken feldspar will usually keep making little trapezoid prisms!
 * This is because there are lines of weakness formed by ionic bonds.
 * The weak planes break, leaving crisp sides to the little baby trapezoids.
 * Feldspar chunks can get sloppy edges.
 * Chemical weathering can attack the edges of feldspar chunks.
 * It's easier to dissolve than is quartz.
 * Tiny sand grains made of feldspar mineral might look a little bit more rounded off than their quartz neighbors.

Where do we find feldspar, and how does it get there?
Feldspar forms naturally, without aid of life, in igneous rocks.


 * Magma that cools slowly, under the earth's surface, can allow feldspar chunks to form.
 * examples include granite, diorite, etc.
 * In these rocks, the feldspar is the opaque bits that look like white chocolate, or have a pink hue.

Feldspar is important in sedimentary rocks.
Sandy beaches in California, Oregon, and Washington include lots of quartz grains, and often an equal number of feldspar chunks.

Feldspar sand grains form by:


 * weathering the original rock where the feldspar formed (see above) - maybe an igneous granite;
 * transporting and breaking the feldspar chunks in a river;
 * further breaking the feldspar chunks as they shift along the ocean beach.

Feldspar CAN get destroyed by enough weathering and erosion!


 * Extremely "mature" sand will have no feldspar, because it's been weathering and eroding for so long.
 * You can tell how "mature" a sand, or the grains in a sandstone, are by:
 * The minerals present
 * How rounded-off the grains of feldspar and quartz look.
 * More angular chunks means fresher grains, less travel, etc.
 * More rounded-off means longer time or space traveled.

Sand can make SANDSTONE in the right conditions. See Depositional Environments to learn more.

Carbonate: Calcite and Aragonite
Calcite and aragonite are the names given to the two most common forms of carbonate minerals. Check out a color 3D model here!

Calcite is made of oxygen, carbon, and calcium.


 * Calcite can be clear or opaque.
 * It can be bright white or a range of dusty warm colors (pink, orange, etc.)
 * It forms as trapezoid prisms - like cubes, but with a distinct lean.
 * You can find big chunks of calcite in the desert mountains around Utah.
 * You can spot cracks in rocks that are filled with calcite mineral pretty much all over the place in Utah.
 * Calcite is easy to scratch and very easy to dissolve, and it will break if hit with a hammer.
 * Calcite is made and destroyed by ionic bonding action!
 * One ingredient is a carbonate ion.
 * It's a covalent-bonded meatball of 1 carbon + 3 oxygen
 * Together, this meatball is sharing TWO extra electrons that they stole from some hapless hydrogen atoms.
 * The extra electrons give the whole meatball a negative charge, so we call it an ion (a charged particle).
 * The other ingredient is calcite ion.
 * This is just one atom of calcium,
 * but it's missing TWO electrons because some other atom or molecule or mineral tore them off.
 * By keeping its protons and neutrons in the nucleus,
 * the calcium is still acting like calcium,
 * but the protons now outmatch the electrons.
 * So the calcium now has a POSITIVE charge of +2,
 * and we call it an ion.

Broken calcite will usually keep making little trapezoid prisms!


 * This is because there are lines of weakness formed by ionic bonds.
 * The weak planes break, leaving crisp sides to the little baby trapezoids.


 * Calcite chunks can get sloppy edges.
 * Chemical weathering peels ions off the edges and corners most easily.
 * If you put acid on calcite, it will fizz.
 * This is why you can clean your sink or humidifier with vinegar to remove crusty build-up from tap water.
 * The fizzing happens because the calcium ions get stripped off, the carbonate ions interact with water, and carbon dioxide goes zipping into gas phase as bubbles.

Calcite can dissolve completely, but the ions can also travel in water and rebuild the mineral some place else!

Where do we find calcite, and how does it get there?
Calcite forms naturally, without aid of life, in sedimentary environments.


 * Ions of carbonate and of calcite can travel in water, then form up wherever they get in high enough concentration.
 * Caves
 * In between grains of sand in a sandstone
 * cracks in other rocks

BUT life is usually around when calcite is forming!!

Sometimes life is DEFINITELY building the calcite.


 * Most "seashells" are made of carbonate minerals, calcite and/or aragonite.
 * Clams build shells out of the ions they harvest from seawater.
 * Land snails build it from ions they harvest from water, soil, air, and their food.
 * Hermit crabs STEAL shells from dead snails, but the crab exoskeleton is crunchy because it, too, harvests carbonate and calcium ions from seawater!
 * Lots of microscopic drifting sea plankton make tiny carbonate Frisbees that build up on the sea floor.

Often, life is kind of around, and it's hard to tell what's happening.


 * Calcite forms layers, piles, spheres, or goo in watery places.
 * These places are usually teaming with bacteria, cyanobacteria, and various gross stuff.
 * It's often hard to tell whether the microbes are making the mineral form, or they're just enjoying the show.
 * Examples:
 * The Great Salt Lake has big crunchy domes, and sand made of tiny calcite spheres called "ooids".
 * Mono Lake exposes big spooky tufa towers made of low-density calcite from when the lake used to be deeper.
 * Any chunks of coral reef or broken shell sand might have carbonate goo forming in the cracks.

Aragonite is probably ALWAYS made by life when it forms on the Earth's surface. It will only form without life if the chemistry and physics are different, like in metamorphic rocks.

Calcite and Aragonite are important in sedimentary rocks.
Sandy beaches in Hawai'i and Florida include lots of carbonate, usually bits of broken sea shells and coral.

Carbonate sand grains can form by:


 * animals make the mineral for their shell;
 * shells get busted by waves;
 * shell bits get more busted as they shift along the ocean beach.

LIMESTONE is what we call rocks mostly made of carbonate, whether they were sandy or gooey originally.

Limestone can metamorphose into MARBLE.