Minerals
1. Mineral- a naturally occurring inorganic solid with a definite chemical composition and an orderly
arrangement of atoms. They are found in rock. The most common rock forming minerals are called
silicates.
a. Characteristics
i. Created naturally by earth processes—either inside the earth or on the surface.
1. Salt—aka “Halite”--forms from evaporation of sea water
a. Evaporation is a natural process occurring on earth without human help.
(Salt evaporated from solution in a lab or in a classroom is not a
mineral—it was done on purpose)
ii. Inorganic—This means no life processes occur in minerals
iii. They have definite chemical composition based on the elements and compounds that
make them up.
1. The mineral halite is made from a compound: Sodium Chloride NaCl—an ionic
bond of sodium and chlorine
iv. Crystalline solids—with definite volumes and shapes. All minerals are solids—but not all
solids are minerals.
2. Structure of Mineralsa. Made from crystals- a solid in which the atoms are arranged in orderly, repeating patterns such
as:
Hexagonal
Cubic
Triclinic
b. Crystals from Magma:
i. Crystals form as magma within the earth cools because the atoms are losing kinetic
energy—they slow down—and move closer together and form compounds.
1. Slow cooling magma generates large crystals—they can be seen with the naked
eye
2. Fast cooling magma generates smaller crystals—they cannot be seen without a
microscope
c. Crystals from Solution
i. Minerals dissolved in water can form crystals
1. Evaporation leaves ions (charged atoms) behind which arrange themselves
naturally into crystals
2. In water, ions are attracted to each other and form crystals without evaporation
3. Mineral Identification through physical properties.
a. Every mineral has unique characteristics that are used to identify them. You cannot only use
one property to identify a mineral.
i. Color—not the only criteria to be used to id a mineral!
1. Ex. Gold and pyrite are both gold in color, but are very different minerals.
ii. Hardness – a measure of how easily a mineral can be scratched.
1. Hardness is determined by how the atoms of a mineral are arranged.
2. Moh’s Hardness Scale—compares mineral strength to common objects that can
leave a scratch mark on them.
a. Finger nail scratches Talc—Talc is very soft.
b. Calcite—can be scratched with a piece of copper—like an old penny.
Calcite is harder than Talc but nowhere near as hard as a diamond.
iii. Luster—The way a mineral reflects light.
1. Metallic—shines like metal
a. Gold / Silver / Copper are metallic.
b. At certain temperatures and pressures metallic minerals can dissolve in
fluids. Mineral rich fluids seep into and between rock layers to form
veins. When this fluid cools, the minerals crystallize and leave deposits
that can be mined. Gold, silver and copper are found in veins.
2. Nonmetallic- Mineral does not shine like metals do. Instead they may look dull,
glassy, pearly, or silky.
a. Ex- quartz is a nonmetallic mineral with a glassy luster
iv. Specific Gravity—aka “Heft”—how heavy a small amount of a mineral is compared with
an equal volume of water.
1. Ex. Gold is extremely heavy compared to water so it sinks. Pyrite looks like
gold, but has a much lower specific gravity.
v. Streak—The color of a mineral in powdered form. Different minerals leave different
colored streaks. Some minerals are too hard to leave a streak.
vi. Cleavage and Fracture—They way a mineral breaks. **Determined by how a mineral’s
atoms are arranged
1. Cleavage-when a mineral breaks in smooth sheets
a. Mica cleaves off in very thin sheets. You can break them with your
fingers.
2. Fracture-when a mineral breaks into uneven, jagged surfaces.
a. Quartz has fracture
vii. Magnetism – Magnetite is magnetic—acts like a magnet.
viii. Radioactivity- Some minerals contain highly unstable elements such as uranium. Over
time, uranium decays and gives off energy called radiation that is very harmful to living
things.
ix. Fluorescence- Some minerals glow in the dark like phosphorus
x. Double Refraction – light passes through the mineral calcite and is bent by the angles of
the crystals producing a double image to the naked eye.
xi. Chemical Reactivity--Reacts with Acid—emits a gas
1. Calcite bubbles and fizzes in the presence of HCl acid as carbon dioxide is
created.
4. Uses—mineral have many uses. Here are a few examples.
a. Jewelry / lasers / industrial abrasives/ cutting tools -gem stones such as diamonds and rubies
b. Electronics/time pieces —quartz
5. Ores —elements that make up the substance of a mineral that are mined for profit. Ores are in many
of the products we use.
a. Hematite-- is a mineral ore is made of the element iron and is used in lots of products from
frying pans to rail road cars and ships.
b. Rutile and ilminite are ores that contain the element titanium—a strong lightweight metal.