Mineral Propertie s
It is often difficult to identify a mineral simply by looking at it, but each mineral has a set of distinctive characteristics that are easil y tested in the field or laboratory. Hardness. Hardness is a distinctive quality of minerals that is determined by the Mohs hardness scale. Talc is the softest
mineral on the scale at a value of 1, and diamond is the hardest at a value of 10 (Table 1) . Geologists
often scratch minerals with a knife blade that has a hardness of about 5 . If the mineral scratche s
the knife, it is harder than 5 ; if the mineral is scratched, its hardnes s is less than 5. A thumbnail is
about 2.5 on the Mohs scale. Most geologists can remember the hardness scale only by using
a mnemonic device (Table 1).
Color. Although color should always be taken into consideration , minerals can frequently occur in a variety of colors . Chemical weathering also changes a mineral's external color. Scraping a mineral on
a porcelain surface, or streak plate, leaves a distinctive colored streak that is more diagnostic of a mineral than its external color. Luster. The luster is the appearance of the light that is reflected from
a mineral's surface . Lusters can be metallic (shiny, like gleamin g metal), glassy or vitreous (glazed like porcelain), or earthy (dull, no t shiny) . Crystal form . Sometimes minerals have a distinctive crystal form that reflects a specific internal arrangement of atoms . The crystal form is best developed when the mineral can crystallize slowly from the fluid that contains its elements . Cleavage. Cleavage is the tendency of a mineral to break along preferred crystalline planes that are weakly bonded
. The angle between various crystal faces is often distinctive for different mineral group sand can be determined with a magnifying lens in the field .Other properties. Other properties useful in mineral identificationare the way a mineral fractures, its specific gravity (estimated by how heavy it feels), and whether it is magnetic or not.
mineral on the scale at a value of 1, and diamond is the hardest at a value of 10 (Table 1) . Geologists
often scratch minerals with a knife blade that has a hardness of about 5 . If the mineral scratche s
the knife, it is harder than 5 ; if the mineral is scratched, its hardnes s is less than 5. A thumbnail is
about 2.5 on the Mohs scale. Most geologists can remember the hardness scale only by using
a mnemonic device (Table 1).
a porcelain surface, or streak plate, leaves a distinctive colored streak that is more diagnostic of a mineral than its external color. Luster. The luster is the appearance of the light that is reflected from
a mineral's surface . Lusters can be metallic (shiny, like gleamin g metal), glassy or vitreous (glazed like porcelain), or earthy (dull, no t shiny) . Crystal form . Sometimes minerals have a distinctive crystal form that reflects a specific internal arrangement of atoms . The crystal form is best developed when the mineral can crystallize slowly from the fluid that contains its elements . Cleavage. Cleavage is the tendency of a mineral to break along preferred crystalline planes that are weakly bonded
. The angle between various crystal faces is often distinctive for different mineral group sand can be determined with a magnifying lens in the field .Other properties. Other properties useful in mineral identificationare the way a mineral fractures, its specific gravity (estimated by how heavy it feels), and whether it is magnetic or not.
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