Some of these minerals are much more abundant than others. Suppose you are excavating for a residential basement and find a very shiny and interesting rock. Your tool shed probably does not have an x-ray diffraction device or a mass spectrometer. Thus, the physical properties that one can identify with the unaided eye and a few simple tools becomes useful. It will be bounded by planar surfaces symmetrically arranged.
Cleavage is the tendency of a mineral to break in certain preferred directions along smooth planes.
Twinning is the intergrowth of two or more single crystals of the same mineral with different geometric orientations. Striations are parallel, threadlike lines or narrow bands running across crystal faces or cleavage surfaces. Hardness is determined by the relative ease or difficulty with which one mineral can scratch another. Using known mineral samples to test the hardness of an unknown is common practice. Specific Gravity is, essentially, the minerals density when compared to the density of water.