The chemical formula of Diaspore is indicated by Al2O3H2O. Diaspore is a hydroxide mineral. It is known to crystallize in the orthorhombic crystal system. In optical mineralogy, the orthorhombic crystal system comprises crystals having three mutually perpendicular axes, of which all are of different lengths. When viewed under petrographic polarizing microscope, Diaspore exhibits a biaxial positive figure. The indices of Diaspore range from 1.700 to 1.750. The birefringence of Diaspore ranges from 0.040 to 0.048. When viewed with the aid of polarizing microscopes used in optical mineralogy, the optic angle of Diaspore is usually within the range of 84 degree to 86 degree. Diaspore also exhibits a high positive relief when viewed in reflected light of polarizing microscopes for mineralogists.
When Diaspore is evaluated using the Mohs scale method, it is usually found having hardness measure ranging from 6.5 to 7. The specific gravity measure of the mineral ranges from 3.3 grams per cubic centimeters to 3.5 grams per cubic centimeters. When examined in hand sample, Diaspore usually appear colored white, gray, or colorless. Sometimes it can be found with shades of green, brown, red, violet, yellow, or pink. When rubbed on a white porcelain streak plate, it is commonly found leaving a white streak. When viewed in reflected light of petrographic polarizing microscope, Diaspore is commonly found exhibiting a vitreous or pearly luster. Diaspore has been also found to decrepitate strongly in a flame.
If evaluated as thin sections or fragments, Diaspore is commonly found colorless. But sometimes, the fragments of colored varieties may show pale colors and pleochroism under polarized microscopes used in optical mineralogy. The crystals of mineral Diaspore are usually tabular or occasionally fibrous, which can be more splendidly exhibited under petrographic polarizing light microscope. It also most commonly occurs as scaly aggregates that are often very fine grained.
When viewed with the aid of polarizing microscopes for mineralogists, Diaspore is commonly found having single perfect cleavage on one direction, imperfect prismatic cleavage on another two direction, and a single poor cleavage on another one direction. Diaspore is not commonly twinned although there can be also some possible occurrence of twinned sections. The extinction of the mineral Diaspore is parallel to the trace of the cleavage in the principal sections. The elongate sections may be either length fast or length slow. This is however depending on how the crystal was cut.
The vivid third-order interference colors in thin sections are usually produced by the high birefringence of the mineral. The interference figures of the mineral are often difficult to obtain due to small grain size. When viewed between crossed nicols of the polarizing microscopes, the cleavage flakes usually yield flash figures. The optic axis dispersion is usually found weak. Diaspore is generally not altered although there can be possible conversion to mineral corundum. This can be possible when Diaspore is heated and dehydrated, or may be with the addition of silica it may form kaolinite or other clay minerals. Diaspore is commonly found in emery deposits and other aluminous metamorphic rocks. It can be also produce by weathering of aluminum-bearing minerals. Diaspore can be also produce by hydrothermal alteration of aluminous rocks.
