San Diego Natural History Museum--Your Nature ConnectionSDNHM Field Guide
Hornblende, collection of the San Diego Natural History Museum. Photo credit: Tim Murray for SDNHM.

Hornblende

From the German words horn, a possible reference color of horn, and blenden, meaning "to deceive," because it resembles some metallic ores.

Description and Occurrence

Hornblende generally forms as stubby, prismatic crystals. It can also occur in massive, compact, granular, columnar, or fibrous habits. Its color ranges from green to greenish-brown to black. A common rock-forming mineral, hornblende can be found in granite, basalt, diorite, schist, and gneiss.

Although hornblende is a common mineral that is found in various rock types, it has almost no commercial value.

Field Notes: Hornblende is generally a greenish-black color and cleaves at 60° and 120° angles. It is sometimes mistaken for black tourmaline, but tourmaline cleaves poorly.


Physical Properties

Color Streak Transparency Luster Hardness Cleavage Fracture Specific gravity Crystal form
green, brown, black none transparent to translucent along the edges vitreous 5 - 6 perfect in two directions, at 60° and 120° angles splintery 3 - 3.4 monoclinic

Photo Credit: Tim Murray for SDNHM

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