Luster - quality and intensity of light that is reflected from the surface of the substance. Hardness - scratchability as indicated by Mohs' hardness scale. A mineral is a set of faces that have a definite geometric relationship. Fracture - some minerals show a conchoidal fracture. Specific gravity - Heaviness or density of the mineral.
Specific gravity is the ratio of the mass of a substance to the mass of an equal volume of water.
Magnetic - Magnetite is an iron oxide which is magnetic. Double refraction - Light splits into two components when it enters some crystalline materials such as calcite. Polymorphs - Those compounds which are known to form two or more different kinds of crystal structures. Important Minerals of the Earth's Crust Silicates are the most important rock forming mineral. All are substances which contain silicon are silicates.