Minerals of Earth’s Crust Chapter 5

What is a mineral? A natural, usually inorganic solid that has a characteristic chemical composition, an orderly internal structure, and a characteristic set of properties Halite

Characteristics of Minerals 1.Inorganic 2.Forms and exists in nature 3.Crystalline solid (atoms are arranged in a regular pattern) 4. Consistent chemical composition Gypsum Fluorite

Mineral or Nonmineral?

Salt? Sugar? Ice? Charcoal? Rock?

Kinds of Minerals Scientists have identified 3,000 minerals Of those minerals, there are 20 common rock- forming minerals All minerals are divided into 2 main groups: Silicate and Nonsilicate Minerals Silicates Nonsilicates

Silicate Minerals Minerals that contain a combination of silicon and oxygen atoms Silicate minerals other than quartz have one or more additional elements such as Ca, Na, K, Fe, or Mg Silicate minerals make up 96% of Earth’s crust Quartz and feldspar make up more than 50% of the crust

Nonsilicate Minerals Minerals that do not contain a combination of silicon and oxygen atoms Nonsilicate minerals make up 4% of Earth’s crust There are 6 major classes of nonsilicate minerals

Classification of Nonsilicate Minerals

How to Identify Minerals Mineralogists identify minerals based on a number of specific physical properties:  Color  Streak  Luster  Cleavage and Fracture  Hardness  Crystal Shape  Density

Color Easy to observe Unreliable on its own Trace amounts of certain elements can greatly effect color of some minerals (ex: sapphires and rubies) Weathering can also cause changes in color Rubies are cut from corundum with traces of Chromium (Cr) Sapphires are cut from corundum with traces of Cobalt (Co)

Streak Color of the mineral in the powder form More reliable than color Use a streak plate: unglazed tile Minerals that are harder than the streak plate will leave no streak

Luster Light reflected from the mineral’s surface Metallic luster reflect light like polished metals All other minerals have nonmetallic luster: waxy, pearly, glassy, dull/earthy, or virtuous/brilliant

Cleavage and Fracture Cleavage is the tendency of a mineral to split along specific planes of weakness to form smooth, flat surfaces Cleavage occurs in one, two, or three directions Cleavage in three directions. Example: CALCITE

Cleavage and Fracture Fracture is when the mineral does not split along cleavage planes Fracture can be irregular, fibrous, or conchoidal

Hardness A measure of the ability of a mineral to resist scratching Hardness does NOT mean resistance to cleavage planes!! Hardness relates to the strength of bonds between the minerals atoms (Ex: Diamond vs. Graphite)

Moh’s Hardness Scale To determine an unknown mineral’s hardness, you need to scratch it against a mineral of known hardness

Crystal Shape A mineral always has the same basic crystal shape because the atoms that make up the mineral always combine in the same geometric pattern There are 6 basic crystal systems that can become more complex due to conditions during formation

Density Ratio of mass to volume of a substance Density = mass/volume Helps identify heavier minerals more readily than it helps identify lighter ones Most minerals have a density between 2 and 3 g/cc Galena Density = 7.6 g/cc Lead Density = g/cc

Special Properties of Minerals Some minerals exhibit special properties that can also be used for identification such as:  Fluorescence  Phosphorescence  Double Refraction  Magnetism  Radioactivity