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Color
Color seems like an easy property but it is risky to identify a mineral
by its color alone. Most minerals can have a wide range of colors due to small amounts of impurities in them such as these examples of quartz.
Smokey Quartz Amethyst Quartz Citrine Quartz Rose Quartz
Another example, rubies and sapphires are the
same mineral, corundum, and have a wide Corundum range of colors! So color alone is not very diagnostic. Streak A mineral’s streak is the color of a powdered mineral on a streak plate (unglazed porcelain tile). This property can be diagnostic for a small number of minerals (usually those with a metallic luster). Although the color of a mineral may vary, the color of the streak remains surprisingly constant. Luster Luster describes the way that the surface of the mineral reflects light. There are many types of lusters but the common ones are: •Metallic •Nonmetallic • glassy • brilliant • dull Hardness Hardness is a mineral’s ability to resist being scratched. The Mohs hardness scale is a unitless 10-point scale with each hardness value represented by a common mineral. The Mohs’ hardness scale is not linear! Hardness can be directly related to bond strength – hardness is an expression of the weakest bond. Compare the hardness of graphite (H=1) and diamond (H=10); they have the same chemical composition but different bonds/structures. Crystal Form Some minerals that grow without being impeded by their environment develop characteristic crystal shapes or crystal form that represents the symmetry of the crystal structure. Crystal form can be a diagnostic property for some minerals.
Quartz has an internal structure
that has a 6-sided (hexagonal) symmetry. As a result, quartz crystals commonly are 6-sided.
Halite has an internal structure that
has a cubic (4-sided) symmetry. As a result, halite crystals commonly 6 are cube shaped. Cleavage Cleavage is the tendency of minerals to break parallel to crystallographic planes along which chemical bonds are weaker than others. Cleavage surfaces are not necessarily parallel to crystal faces. It may be difficult to distinguish between cleavage planes and crystal faces. biotite albite halite calcite fluorite Fracture Fracture is the way a mineral breaks in the absence of a cleavage plane. In some crystals, the strength of bonds is approximately equal in all crystallographic directions. Several types of fracture can be described: conchoidal – smooth curved surfaces resembling shells fibrous – common with asbestos hackly – jagged fractures with sharp edges irregular or uneven – rough or irregular surfaces
Conchoidal fracture in Fibrous fracture in Hackly fracture in native
obsidian. chrysotile. copper. Chemical Properties of Minerals James Dana • The first person to use the classification of minersl in 1848. 8 Basic classes of minerals: • Silicate Class • Carbonate Class • Sulphate Class • Halide Class • Oxide Class • Sulphide Class • Phosphate class • Native element class Silicate Class • largest and most abundant group. • mostly contains Si and O. • ex. Feldspar, quartz, pyroxene, mica, olivine, and amphibole. Carbonate Class • mostly found deposited in marine environment. • these are formed from the shells of dead plankton and other marine organisms. • it includes nitrate and borate minerals. Sulphate • forms in areas with high evaporation rates and where salty waters slowly evaporate. • ex. Anhydrites, celestine, barite, and gypsum. Halide • contains natural salts, flourite, halite, sylvite and sal ammoniac components. • usually from lakes and ponds. • these are relative low hardiness, transparent, have good cleavage, low specific gravity, and poor conductor of heat and electricity. Oxide class • Metallic minerals such as hematite and gemstones. • these minerals are important as they carry histories of changes in Earth’s Magnetic field. Sulphide • important metals such as copper, lead and silver. • these are metals found in electrical wires, industrial materials, and other construction materials. Phosphate • Contains phosphorus. • important biological mineral found in the teeth and bones of many animals. • Arsenic • Phosphate • Vanadium Native elements • metals and intermettalic elements • Gold, silve, copper • semimetals • Nonmetals • Antimony, bismuth, graphite, sulphur • natural alloys • Raw meteorites