Mineral

a naturally occurring inorganic solid with a distinct chemical composition and crystalline

structure

Formation

Magma

Pressure

Evaporation

Magma

When minerals form out of molten rock, or magma. As the magma cools, the atoms move closer together and

form chemical bonds, creating compounds. Many different minerals may form from one bed of magma.

Pressure

When a rock is subjected to high temperature and pressure, the minerals in the rock break down

chemically WITHOUT melting, creating new minerals.

Evaporation

When minerals form as water containing dissolved ions slowly evaporates. For example, halite forms when water evaporates from a solution of salt and water.

Characteristics

The characteristics of a mineral can help you figure out which mineral a sample is. For example:

Cleavage/Fracture Crystal structure

Luster Streak

Hardness Specific Gravity

Color Other properties

Crystal Structure

Cubic3 equal-length axes of symmetryAll 90° anglesHalite / Pyrite

Crystal Structure

Tetragonal3 axes of symmetry: 2 same length, one

differentAll 90 ° anglesZircon

Crystal Structure

Hexagonal4 axes of symmetry3 same length at 120° angle1 different length at 90° angleQuartz

Crystal Structure

Orthorhombic3 unequal axes of symmetryAll 90° anglesTopaz

Crystal Structure

Monoclinic3 unequal axes of symmetryTwo at 90° angles, one notGypsum / Calcite

Crystal Structure

Triclinic3 unequal axes of symmetryNo 90 ° anglesFeldspar

Cleavage

the tendency of a mineral to split along planes of its crystalline structure where bonds are weakest; some minerals break only in one direction, others break in two or more directions

Cleavage

Cubic: form cubes

HalitePyrite

Cleavage

Rhombohedral: form six-sided prisms

Calcite

Cleavage

Basal: occur along a single plane parallel to the base (flat layers)

Mica

Fracture

the property of a mineral that describes an irregular pattern of breakage in a direction other than along cleavage planes; i.e. when a mineral does not break along flat planes

Fracture

Conchoidal Fracture: smooth, curved fracture like the inside of a clam shell

Obsidian Quartz

Fracture

Fibrous/Splintery Fracture: looks like splinters

Asbestos

Luster

The property of a mineral that describes the appearance of light reflected from its surface

Metallic (looks like a metal)Pyrite Hematite

Luster

Vitreous (glassy)

Quartz

Emerald

Luster

Adamantine (brilliant)

Diamond

Luster

Resinous (like resin or sap from a tree)

Sphalerite

Luster

Greasy or waxy

Turquoise

Luster

Pearly

Talc

Luster

Silky

Asbestos

Luster

Dull or earthy

Limonite Bauxite

Colorthe least important property of a

mineral, since chemical impurities can change the color of the same mineral

Quartz

Iron (Fe)

•Aquamarine = blue

•Heliodor = yellow

•Green beryl

Manganese (Mn)

•Morganite = pink

•Red beryl = red

Chromium (Cr)

Emerald = emerald green

The Colors of Beryl

beryllium aluminum silicate

impurities of different elements or ions change the color of a mineral

Corundum: Aluminum oxide

Ruby corundum has both chromium and iron impurities, making it red.

Sapphire corundum can be many colors, including purple, green, pink, orange, yellow or blue, depending on the amounts of iron and titanium.

Streak

the property of a mineral that describes its color in powdered form

Streak

When a mineral is rubbed firmly across an unglazed tile of white porcelain (a streak plate), it leaves a line of powder. This is called the streak. The color of the streak is always the same, whether or not the mineral has impurities. For example, quartz leaves a white streak, whether it's violet (amethyst), pink (rose quartz), or brown (smoky quartz).

the resistance of a material to scratching

HardnessRating Reference Material Reference Tool

1 Talc  

2 Gypsum Fingernail (2.5)

3 Calcite Copper penny (3.5)

4 Fluorite  

5 Apatite Glass plate (5.5)

6 Potassium feldspar Steel file (6.5)

7 Quartz  

8 Topaz  

9 Corundum  

10 Diamond  

Specific Gravity

the ratio of the weight of a substance to the weight of an equal volume of water

Specific Gravity = Weight in air

Weight in air – Weight in water

Other Propertiesany other special property of a mineral that distinguishes it

from others

Magnetic: affects a compass (example magnetite)

Double refraction: when a mineral splits the light rays that pass through it, making a single object appear as two objects when you look through the mineral (example calcite)

Other Properties

Fluorescent: when a mineral glows under an ultraviolet light (example fluorite)

Salty taste: when a mineral tastes like salt (example halite) DO NOT TEST YOUR MINERALS FOR THIS!!!

Radioactive: when a mineral gives off subatomic particles that are detected by a Geiger counter (example uraninite)