PROPERTIES OF
MINERALS
Physical and Chemical
CHEMICAL COMPOSITION
• Nearly all of Earth’s crust (98.5%) is made up of only eight elements:
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Oxygen
Silicon
Aluminum
Iron
Calcium
Sodium
Potassium
Magnesium
• All minerals have a specific chemical composition: The mineral silver is composed only of
silver atoms, while diamonds are composed only of carbon atoms.
• But most minerals are made up of a mixture of different chemical compounds. Each
mineral has its own chemical formula. (I.e. Table Salt: NaCl)
WHAT ISN’T A MINERAL?
• Glass, though made ultimately of sand, which is rich in mineral quartz, is not a
mineral. It is not crystalline. Glass has, instead, a very random assemblage of
molecules.
• Steel is made by mixing different metal minerals like iron, cobalt, chromium,
vanadium, and molybdenum. But steel is not a mineral because it is forged by
humans and therefore not naturally occurring.
• However, almost any rock you pick up is composed of minerals.
WHAT PROPERTIES ARE USED TO IDENTIFY
MINERALS?
• Scientists have identified more than 4,000 minerals in Earth’s crust. Most minerals can be
identified with little more than the naked eye and a few tests.
• We do this by examining the physical properties of he mineral in question, which include:
• Color: the color of the mineral
• Streak: the color of the mineral’s powder (this is often different from the color of the whole
mineral)
• Luster: shininess
• Density: mass per volume, typically reported in “specific gravity,” which is the density relative
to water.
• Breakage: how a mineral breaks
• Cleavage: the mineral’s tendency to break along planes of weakness
• Fracture: the pattern in which a mineral breaks
• Hardness: what minerals it can scratch and what minerals can scratch it