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Amblygonite: A
Fluo-phosphate of Aluminium and Lithium. This mineral forms large
ill-defined triclinic crystals, and compact masses with a columnar
cleavage. Its color is white, gray, or a very light tint of blue, pink
or yellow. It is found in granite veins associated with other lithium
compounds, in Saxony, Norway, France; also in Maine, California and
South Dakota.
This
mineral is the principal source of Lithium Compounds in the United
States, and is used in making mineral water; also in photography and
pyrotechnics.
Amethyst: The
transparent purple or violet variety of Quartz. It is the most popular
and valuable of the quartz gems, the deep purple colors being the most
highly prized.
Amphibole: The
amphiboloids embrace a large number of minerals, and the compositions
vary, (see Tremolite, Acti-nolite, Nephrite, Asbestos). It is used for
ornamental
purposes by the Orientals.
Amphibole is a very common and important rock constituent
especially in the building stone rocks and granites; the long-bladed
crystals tie together and render homogeneous the other rock mineral
grains. This mineral is a source of asbestos.
Analcite: Hydrated
Silicate. This mineral has a glassy luster, is transparent or
translucent, colorless or white, gray, yellowish, greenish or reddish.
Analcite resembles Leucite and light colored Garnets, but is
distinguished from Garnets by its hardness, and from Leucite by the
presence of water and easy fusibility. It occurs at Sterling Hill, N.
J.; near Yonkers, N. Y.; in the Lake Superior region and in Colorado.
Anatase: Titanium
Oxide. Oxygen 40%, Titanium 60%. Both Anatase and Brookite have the
same empirical composition which is similar to Rutile. The crystals
are usually sharp pyramidal, and twins are common. This mineral occurs
in Russia, France, Switzerland, and in the diamond fields of Brazil.
Andalusite: Anhydrous
Orthosilicate. Rare semi-precious stone somewhat resembling Alexandrite
in its property of appearing in different colors when viewed in
different
directions. When clear it is used as a gem stone.
Some
specimens contain inclusions of a dark gray or black material,
arranged in such a way as to give a cross-like figure in cross sections
of crystals. Because of the shape of these figures, this variety
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