Throughout the Black Rock area in Nevada one finds every conceivable rock you can think of.  Just about all of us have no idea what we are looking at.  Our rock collecting is picking up "monkey rocks', those shiny or neat looking peices everywhere.  In reality we come across all sorts of interesting things we actually take for granite -granted. This glossary defines many of the rocks we find with accurate descriptions and sometimes photos. Most of these rocks have crystal formations associated with them; which we do not cover. It is not intended to be a Geology Lesson.

A-C  •  D-F • G-I  • J-L  • M-O  • P-R  • S-U  • V-X  • Y-Z

MALACHITE - is a copper carbonate hydroxide mineral. This opaque, green banded mineral crystallizes in the monoclinic crystal system, and most often forms botryoidal, fibrous, or stalagmitic masses, in fractures and spaces, deep underground, where the water table and hydrothermal fluids provide the means for chemical precipitation. Individual crystals are rare but do occur as slender to acicular prisms. Pseudomorphs after more tabular or blocky azurite crystals also occur. Malachite often results from weathering of copper ores and is often found together with azurite, goethite, and calcite. Except for its vibrant green color, the properties of malachite are similar to those of azurite and aggregates of the two minerals occur frequently. Malachite is more common than azurite and is typically associated with copper deposits around limestones, the source of the carbonate.
NITER - is the mineral form of potassium nitrate, also known as saltpeter in America or saltpetre in other English-speaking countries. Niter is a colorless to white mineral crystallizing in the orthorhombic crystal system. It usually is found as massive encrustations and efflorescent growths on cavern walls and ceilings where solutions containing alkali potassium and nitrate seep into the openings. It is produced by nitrification in soil, and used in gunpowders, fertilizers, and preservatives. It occasionally occurs as prismatic acicular crystal groups, and individual crystals commonly show twinning.
OPAL - is a hydrated amorphous form of silica (SiO2·nH2O); its water content may range from 3 to 21% by weight, but is usually between 6 and 10%. Because of its amorphous character, it is classed as a mineraloid, unlike crystalline forms of silica, which are classed as minerals. It is deposited at a relatively low temperature and may occur in the fissures of almost any kind of rock, being most commonly found with limonite, sandstone, rhyolite, marl, and basalt. The internal structure of precious opal makes it diffract light; depending on the conditions in which it formed, it can take on many colors. Precious opal ranges from clear through white, gray, red, orange, yellow, green, blue, magenta, rose, pink, slate, olive, brown, and black. Of these hues, the black opals are the most rare, whereas white and greens are the most common. It varies in optical density from opaque to semitransparent. The term opalescence is commonly and erroneously used to describe this unique and beautiful phenomenon, which is correctly termed play of color.

A-C  •  D-F • G-I  • J-L  • M-O  • P-R  • S-U  • V-X  • Y-Z