This garden variety mineral is an Inosilliicate. IT has prismatic crystals and often times they are accompanied with hexagonal cross section and twinning. It has about a hardness of a steel nail. It is black, green, or greenish brown in color, but its streak is often a white to gray. It occurs in igneous rocks yet is is found in metamorphosed rocks in the form of schist and amphibolite. This mineral is insoluble in acid. This mineral is very widespread in Sweden. Hornblende’s generalized chemical formula is (Ca,Na)2(Mg,Fe,Al)5(Al,Si)8O22 (OH)2.