Hornblende

Hornblende is one of the basic silicate minerals. Its composition is Ca₂(Mg,Fe,Al)₅(Si,Al)₈O₂₂(OH)₂. Hornblende is the most common example of the group of silicates called amphibole. The sample above left is about 12x8 cm and is from Ontario, Canada. The sample above right is about 3x3 cm and is from Russell, New York. The samples are on display in the Smithsonian Museum of Natural History.

Hornblende has two cleavage directions that intersect at roughly 60° and 120°. It is usually dark green to black in color and is similar to augite. It is commonly found in continental rocks which are igneous in origin. It often makes up the dark part of rocks which are composed of light and dark crystals.