Adopt-a-Mineral Project:
Orthoclase
by Robby Flood

www.emporia.edu/earthsci/amber/
go336/flood/

Mineral Twinning
by Robby Flood

www.emporia.edu/earthsci/amber/
go336/flood/twin.htm

Adopt a Mineral Project: Orthoclase
by Robby Flood

www.emporia.edu/earthsci/amber/go336/flood

This webpage project was created for a mineralogy course at Emporia State University. The first mineral I adopted was orthoclase and a summary of this mineral follows.

Wenk and Bulakh (2004) define a mineral as naturally occurring, macroscopically homogeneous chemical compounds with a regular crystal structure (p. 3). The study of these substances fits under the broad discipline of mineralogy. Research on minerals has been around since the time of the Greeks, and since then many men have made important discoveries in the field.

The most abundant class of minerals in the Earth’s crust is the silicate class (http://mineral.galleries.com/minerals/silicate/class.htm). The moon is also made of similar minerals. Among this class is a subgroup known as the alkali feldspars and orthoclase is one of the minerals common to this subgroup. With a chemical formula of KAlSi3O8, one can see both the potassium and the silica (Chesterman 508).

White, pink, brown, gray, green, and yellow are the common colors associated with this mineral, which can also be colorless. It streaks white and the luster is vitreous on fresh surfaces. Orthoclase is the indicator mineral on Mohs Hardness scale at 6, making it a fairly hard mineral.

There is a good two-directional cleavage at 90 degrees. Orthoclase is in the monoclinic crystal system. Carlsbad twinning may occur in which one crystal is rotated 180 degrees about the axis (Wenk and Bulakh 329). This mineral is primarily found in metamorphic and intrusive rocks such as gneiss and granite,respectively. Uses for orthoclase include a glaze in ceramics, mild abrasive, and gemstone (mineralgallery.com). A milky translucence is the phenomenon that makes this subgroup in the feldspars sufficiently interesting to be a gemstone.

References


For more information email rflood@emporia.edu.

Return to GO 336 Student webpages, www.emporia.edu/earthsci/amber/go336/webpages.htm.