Physical Geology 101
Mineral Systems and Physical Properties
Mineral Physical Properties
Physical aspects of a mineral.
Based on chemical composition and crystalline structure.
Most obvious physical property.
Most deceptive physical property.
Most minerals can have more than one color.
Controlled by chemical composition - different chemicals result in different colors.
The color of a mineral that is powdered.
Streak color of a mineral shows less variation than the Color.
Most minerals have only one streak color.
All minerals have a streak color.
Controlled by the chemical composition.
Ability of a mineral to resist abrasion.
Controlled by the crystalline structure and the type of chemical bonds.
stronger bonds = harder mineral
Mohs Scale of Hardness
Minerals are ranked on a scale of 1 to 10
1 is the softest; 10 is the hardest
Mineral shape, if the mineral is allowed to grow unrestricted.
Controlled by crystalline structure.
Not very useful for mineral identification.
many minerals have more than one crystal form.
well developed crystals are relatively rare.
Tendency of a mineral to break along a plane of weakness within crystalline structure.
Controlled by crystalline structure and chemical bonding.
0, 1, 2, 3, 4, and 6 cleavage planes can exist.
Most difficult physical property for students to understand and identify.
Similar to cleavage
Manner in which mineral breaks, but not along a plane of weakness.
Conchoidal fracture - break looks like broken glass.
Controlled by crystal structures and chemical bonding.
All minerals have fracture.
Appearance and intensity of light reflected from mineral surface.
Two main groups.
Metallic - looks like metal.
Non-metallic - doesn't look like metal.
Controlled by chemical composition and crystal structure.
Generally, not very useful for identification.
Other Physical Properties
Specific Gravity - ratio of the mass of a given volume of mineral to the mass of an equal volume of water
Hydrochloric acid - HCl - Click here to see an short animation (MPG file - 351 Kb)
Radioactivity - Example showing the detection of radioactivity using a Geiger Counter in a sample containing the radioisotope thorium.
Minerals can be grouped together based on similarities in chemical composition and crystalline structure
Pseudomorphs are minerals that take the form of another mineral.
Quartz has a hexagonal crystal.
Quartz will form a cubic crystal if it replaces halite.
Minerals can be grouped together based on similarities in chemical composition and crystalline structure.
Single Chain Silicates
Double Chain Silicates
Rock Forming Minerals
Augite - Dark or dull green color, 2 cleavages at ~90 degrees, similar properties to Hornblende
Biotite - Black color, one perfect direction of cleavage resulting in the mineral pealing into thin, flexible sheets, similar properties to Muscovite
Calcite - H=3, reacts with HCl, 3 directions of cleavage (rhombic cleavage)
Fluorite - H=4, 4 directions of cleavage, often purple in color (can be white, clear, yellow, green)
Garnet - Typically reddish brown color, no cleavage, commonly found in twelve-sided crystals (dodecahedrons)
Graphite - "Pencil lead", soft metallic mineral, gray streak
Gypsum - H=2, can be scratched with a fingernail
Halite - "Salt", H=2.5, cannot be scratched with a fingernail, 3 directions of cleavage (cubic), salty taste
Hematite - Reddish brown streak, "rust"
Hornblende - Black to dk. green color, 2 directions of cleavage at 120 or 60 degrees, similar properties to Augite
Magnetite - Magnetic, metallic mineral
Muscovite - Clear or translucent color, one perfect direction of cleavage resulting in the mineral pealing into thin, flexible sheets, similar properties to Biotite
Olivine - Apple green or yellowish green color, H=7 (often difficult to determine), conchoidal fracture, no cleavage
Orthoclase - H=6, salmon pink color is typical, perthitic intergrowths are common, 2 directions of cleavage at 90 degrees, similar properties to plagioclase
Plagioclase - H=6, white or gray color, striations may be seen on cleavage surface, 2 directions of cleavage at 90 degrees, similar properties to orthoclase
Pyrite - "Fool's Gold", gold metallic color
Quartz - H=7, conchoidal fracture, no cleavage, color is typically white or clear but can be pink, red, purple, black
Additional information and identification exercises can be found at:
Mineral Physical Properties and Mineral Identification