Hornblende

Hornblende By: Karsen Houck and Amy Isvik Hornblende is made of Calcium, Magnesium, Iron, Aluminum, Silicate, and Hydroxide. The scientific formula for Hornblende is Ca 2 ﻿(Mg, Fe, Al) ﻿5 ﻿(Al, Si) 8 ﻿(OH) ﻿﻿2. Hornblende﻿ is almost always black or dark green. It's luster varies between vitreous and dull. Hornblende is usually opaque but in some cases there are very thin crystals or very exceptional specimens are translucent. A special characteristic of Hornblende can be seen in these translucent specimens. In these specimens you can notice the pleochroism. This means that they vary in color or shade depending on where you are looking from. In some minerals this trait is very noticeable, in others it is barely observable.

The crystals are monoclinic, the shape of which is shown below. The hardness, rated on the Moh's Hardness Scale (shown below), varies between 5 and 6.

The cleavage of Hornblende is perfect in two directions at 60 and 120 degree angles. Hornblende has an uneven, splintery fracture. The streak is usually brown or gray or a combination of both. The density of Hornblende is usually between 3 - 3.4 g/cm3. Hornblende can be seen through-out the world. Hornblende is often found in metamorphic and igneous rocks. It is not normally found in Iowa. Hornblende is used mainly as a mineral specimen, though it could be found in a collection, but it's not-so-attractive appearance and rarity of "good" crystals makes this rare. No industrial or commercial uses have been found for Hornblende. It is simply an example of what a mineral is.

media type="file" key="Hornblende.m4v" align="right" width="300" height="300" Sources: http://www.galleries.com/minerals/silicate/hornblen/hornblen.htm [| http://www.mindat.org/min-1930.html] @http://www.galleries.com/minerals/property/pleochro.htm @http://www.khulsey.com/jewelry/crystalline_structures.html @http://invsee.asu.edu/nmodules/engmod/prophardness.html @http://www.sdnhm.org/fieldguide/minerals/hornblende.html @http://opticalmineralogy.com/the-silicates-mineral-class/hornblende/ @http://www.pitt.edu/~cejones/GeoImages/1Minerals/1IgneousMineralz/Amphiboles.html @http://www.igsb.uiowa.edu/Browse/minerals/minerals.htm