Content• Crystal Form• Luster• Color• Streak• Hardness• Cleavage• Fracture • Specific Gravity

Physical properties of minerals

• Primary diagnostic properties• Determined by observation or performing a

simple test• Several physical properties are used to identify

hand samples of minerals

Physical properties of minerals

• Crystal form• External expression of a mineral’s internal

structure• Often interrupted due to competition for space

and rapid loss of heat

Crystal System

Cubic crystals of pyrite

A garnet crystal

Physical properties of minerals

• Luster• Appearance of a mineral in reflected light• Two basic categories–Metallic– Nonmetallic

• Other descriptive terms include vitreous, silky, earthy, waxy or others ..

Pyrite displays metallic luster

Kaolinite displays earthy luster

Quartz displays vitreous luster

Satin spar displays silky luster

Jade displays Waxy luster

Physical properties of minerals

• Color• Generally unreliable for mineral identification• Often highly variable due to slight changes in

mineral chemistry• Exotic colorations of certain minerals produce

gemstones

Quartz (SiO2) exhibits a variety of colors

Trace ions give glass its distinctive Trace ions give glass its distinctive colorscolors

Physical properties of minerals

• Streak• Color of a mineral in its powdered form

Small amounts of an impurity that strongly absorbs a particular wavelength can radically change the wavelengths of light that are reflected by the specimen, and thus change the apparent color. However, when the specimen is dragged to produce a streak, it is broken into randomly oriented microscopic crystals, and small impurities do not greatly affect the absorption of light.

Streak is obtained on an unglazed porcelain plate

Hematite

Physical properties of minerals

• Hardness• Resistance of a mineral to abrasion or

scratching• All minerals are compared to a standard scale

called the Mohs scale of hardness

Mohs scale Mohs scale ofof

hardnesshardnessMohs scale relates the hardness of minerals with some common objects, such as fingernails, copper pennies, a steel knife blade, and glass.

Physical properties of minerals

• Cleavage• Tendency to break along planes of weak

bonding• Produces flat, shiny surfaces• Described by resulting geometric shapes– Number of planes– Angles between adjacent planes

Common Common cleavagecleavagedirectiondirection

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Fluorite, halite, and calcite all exhibit perfect cleavage

Schematic diagram of the crystalline structure of Schematic diagram of the crystalline structure of sodium chloridesodium chloride, more commonly known as table , more commonly known as table salt. The actual ions are very closely packed.salt. The actual ions are very closely packed.

Physical properties of minerals

• Fracture• Absence of cleavage when a mineral is broken

Physical properties of minerals

• Specific Gravity• Weight of a mineral / weight of an equal

volume of water• Average value = 2.7

Physical properties of minerals

• Other properties• Magnetism• Reaction to hydrochloric acid• Malleability• Double refraction• Taste• Smell• Elasticity