Final answer:
Corundum can be identified by its hardness (9 on the Mohs scale), hexagonal crystal habit, no cleavage, specific gravity (3.9 to 4.1), and refractive index (1.762 to 1.770). It does not typically fluoresce and has a variety of colors due to impurities, with common varieties being blue sapphires and red rubies.
Step-by-step explanation:
To identify corundum using its diagnostic properties, you would look for its outstanding hardness, which is a 9 on the Mohs scale. This means it can scratch nearly all other minerals, including glass. Corundum has no cleavage but displays a hexagonal crystal habit. Its specific gravity (SG) typically falls between 3.9 and 4.1, and it has a high refractive index, ranging from 1.762 to 1.770. Corundum comes in various colors, including blue (sapphire) and red (ruby), but these are not reliable identification characteristics since impurities can cause color variations. Furthermore, corundum typically does not show fluorescence under UV light.
To assess whether a mineral specimen is corundum in the field, one would first test its hardness against a known reference. If the sample scratches other substances with a lower rating on the Mohs scale, that would be a strong indication of corundum. Secondly, one would look at the physical characteristics of the mineral, including its lack of cleavage and hexagonal habit. If available, measuring the specific gravity and refractive index can also provide confirmatory evidence. However, in many field settings, personal observations such as hardness and crystal habit are the most practical means to identify corundum.