Earth Science Laboratory
EAS 100-51
Physical Properties of Minerals
Physical Property
Materials Used For Testing
Mohs' Hardness Hardness measures the resistance of a mineral to being scratched. The Mohs' Hardness Scale ranges from 1 to 10. Objects of equal hardness can also produce a scratch with greater effort (like grinding a diamond with diamond dust).  Hardness may be determined to the nearest half number using common materials (listed in next column). Fingernail (H = 2.5)
Copper penny or copper wire (H = 3.0)
Glass plate (H = 5.0-5.5)
Steel file (H = 6.0-6.5)
Color The color of a mineral is often variable, and therefore is often unreliable for mineral identification. Eyesight
Streak Streak is the color of a powdered mineral, produced by grinding a corner of a mineral specimen across a porcelain tablet called a streak plate. Streak is more consistent than the color of a whole mineral.  (Minerals with a hardness greater than the streak plate have no streak.) Streak plate (porcelain tablet)
Luster The appearance or quality of light reflected by the surface of a mineral, either metallic or non-metallic. (Tip: Minerals with metallic luster are always opaque - never translucent or transparent.) Eyesight
Taste Most minerals have no particular taste, or they may taste bitter. Halite has a distinctive salty taste. (This test has limited value.) Tongue
Odor Some minerals emit odors only when breathed upon, rubbed, scratched, pounded, or heated. (This test has limited value.) Nose
Feel Some minerals, especially those that are very soft, feel slippery or greasy (such as talc or graphite) because they are softer than your skin. Hands
Acid Reaction Hydrochloric acid reacts only with 2 groups of minerals, the carbonates (effervescence of carbon dioxide gas bubbles), and the sulfides (release of hydrogen sulfide gas, which has the odor of rotten eggs). Not all carbonates and sulfides react with acid to the same degree. Dilute hydrochloric acid (in dropper bottle)
Magnetism Only certain metallic minerals react to a magnet. Magnetite is strongly magnetic. (Not all iron-containing minerals are magnetic.) Magnet
Specific Gravity Specific gravity is the density of a mineral compared to the density of water (which is assigned a value of 1.) Metallic minerals tend to be heavier than non-metallic minerals of the same volume. Only a visual estimate is required in this class; compare the weights of similar sized mineral specimens.
Cleavage The natural tendency of a mineral to break along planes of weak bonding between atoms; this is seen as a smooth flat cleavage plane produced upon breaking the mineral.  Not all minerals show cleavage, so don't look for it if it isn't fairly obvious. Your instructor will display pieces of previously broken minerals. Do not break your mineral specimens!
Fracture The irregular breakage of a mineral whose atoms have strong bonds (lacks cleavage). Some types of fracture have a distinctive pattern, such as conchoidal fracture in quartz. Your instructor will display pieces of previously broken minerals. Do not break your mineral specimens!

Copyright © 1984 by William K. Tong