Hornblende is a group of fairly hard black, green, or brown minerals. Hornblende crystals often appear dark and dull. Less common samples have long, slender crystals with some shiny surfaces. Hornblende forms a major part of many igneous (volcanic) rocks and metamorphic rocks (rocks that have been changed by heat and pressure). See Rock (Metamorphic rock).
Hornblendes are silicates, minerals made up mostly of silicon and oxygen. Hornblende is the most common amphibole, a group of silicates containing calcium, magnesium, and other metals.
In addition to silicon and oxygen, hornblendes contain varying amounts of aluminum, calcium, hydrogen, iron, and magnesium. Many types of hornblende also have small amounts of fluorine, potassium, sodium, and titanium.
See also Schist.
