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 (SiO 2 ) exhibits a variety of colors

Trace ions give glass its distinctive colors

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 of hardness Mohs 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

Commoncleavagedirections

Fluorite, halite, and calcite all exhibit perfect cleavage

Schematic diagram of the crystalline structure of sodium chloride, more commonly known as table 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