Any element not underlined must be present in an appreciable quantity. Other possible element replacements not mentioned may exist but only occur insignificantly or rarely. This field is absent by minerals without a varient formula. Crystal Forms and Aggregates Describes the crystal system , crystal forms , and crystal aggregates of the mineral. Trigonal minerals, which really belong to the hexagonal system, are written grouped together with all the other hexagonal minerals.
Specific gravity is measured by the relative comparison weight of water.
For example, if a mineral has a specific gravity of 3.6, than that mineral is 3.6 times heavier than water. Luster Describes the luster of the mineral Cleavage Describes the mineral's cleavage . Cleavage is measured in this guide by quality and the amount of sides that have cleavage. If all sides have the same cleavage, than all sides is written instead of a number. So a mineral with a cleavage of 1,2 has perfect cleavage in 2 directions.