Morphological crystallography refers to the study of the external form, or morphology, of crystals. Crystallization Crystals are formed from solutions, melts, and vapours. The atoms in these disordered states have a random distribution but with changing T, P, and concentration they may join in an ordered arrangement characteristic of the crystalline state. The physical properties of minerals are a direct result of their chemical and structural characteristics. Many physical properties can be determined by inspection or by relatively simple tests, and as such are important in the rapid recognition of minerals.
Parting is like cleavage, but only occurs along planes of structural weakness in twinned crystals.
Fracture refers to the way minerals breakalong an uneven surface when they do not yield along cleavage or parting surfaces. The habit or appearance of single crystals as well as the manner in which crystals grow together in aggregates are of considerable aid in mineral recognition. Terms used to express habit and state of aggregation are given below. Misellaneous Miscellaneous terms are stalactitic, concentric, pisolitic, oolitic, banded, massive, amygdaloidal, geode and concentric. Hardness A series of 10 common minerals was chosen by F. Mohs in 1824 as a scale, by which the relative hardness of any mineral can be told.