mineral is a naturally occuring, homogeneous, solid with a crystalline atomic structure. Crystallinity implies
that a mineral has a definite and limited range of composition, and that the composition is expressible as a chemical
formula. Some definitions of minerals give them as inorganic materials, however both diamonds and graphite are considered
minerals, and both are primarily comprised of carbon, which would make them organic. So this leads me, as an
engineer, to believe that mineralogists do not have a good, precise definition of a mineral, but rather a loose
definition. The definition above, is the most inclusive and would include all substances currently described as minerals.
The key items that make something a mineral are occurring naturally, and the definite crystal structure, that is
expressible as a chemical formula. Rocks that do not meet this criteria are referred to as amorphis - not having a
definite structure or expressible as a chemical formula. Some elements that occur naturally and are minerals are arsenic,
bismuth, platinum, gold, silver, copper, and sulphur.
THE DEFINITION OF ORGANIC: Organic chemistry is the study of those substances containing carbon in combination with
hydrogen (H), and a few other non metals, namely oxygen (O), nitrogen (N), sulfur (S) and the halogens (F2, Cl2,
Br2, and I2).
Anorthite is a lime feldspar, triclinic, has a hardness f 6 to 6.5 mhos, SG of 2.7 - 2.8, is white, usually, can be colorless
or grayish, bluish, yellowish or reddish. It is transparent to translucent and usually has small amounts of sodium and/or
magnesium, potassium and iron. It is associated with biotite, hornblendes and pyroxenes. It has few uses, commercially, but is used in ceramics, and
lately, in cements, as it has co CO to give off CO2 in the cement process. It is a rare mineral, though, so quantities are limited.
The statement below explains the altered anorthite in the photo, actually mined in Los Angeles county.
North Star Minerals Inc. mines a highly altered Anorthosite.
Anorthosite* is a mono-mineralic rock type. Consisting of more than ninety percent plagioclase feldspar. This rock type forms batholitic
complexes of pre-cambrian and older ages.
The mineralogy of Anorthosite is over 90% plagioclase feldspar of the Labradorite to Bytownite composition. Accessory minerals include
magnetite and Illmenite other minerals have been observed
in smaller amounts but not in all Anothosites.
Alteration minerals include feldspar grains that have turned white due to alteration. Feldspar altering to the Zeolite mineral Laumontite.
Laumontite altering to the Kaolin group clay minerals Halloysite and meta-Halloysite
All the minerals in this hydrothermally altered rock increased the alumina content of this altered Anorthosite.
*note The mineral name for the calcuim end member feldspar is Anorthite. The similarity explains the confusion between rock and mineral names.
Mr. Larie K. Richardson
North Star Minerals, Inc.
501 South First Avenue, Suite N
Arcadia CA 91006-3888
Tel: 626.821.9630 Fax: 626.821.9635
Flash video of anorthite as seen under a microscope will play. May have to click on browser "Allow Active X blocked content" to play
A flash video at right, is the altered anorthite, particles below 100 microns,
submerged in water to reduce glare, filmed through a microscope.
This specemin is from North Star Minerals, a Southern California Clay Mine.