Minerals of Earth’s Crust Chapter 5
Dec 16, 2015
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 Minerals1. Inorganic
2. Forms and exists in nature
3. Crystalline solid (atoms are arranged in a regular pattern)
4. Consistent chemical composition
Gypsum
Fluorite
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
SilicatesNonsilicates
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
How to Identify Minerals
Mineralogists identify minerals based on a number of specific physical properties:ColorStreakLusterCleavage and FractureHardnessCrystal ShapeDensity
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 = 11.35 g/cc