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Title: a book title 'The Basics of Geology'
The world is a diverse place. Its stones are no exception. The number of
minerals discovered is staggering. It is well known that many minerals
occur in only certain terrains, but are there other factors involved in
their distribution? Experienced prospectors would say 'yes'.
Rocks are made from various simplier materials. The more abundant these
materials are in a location, the more abundant are the minerals made from
them. The general ratio of base materials in rocks in relation to one
another in a given area is refered to as a locations's "geology".
Hydrothermal geology is rare, but it is the easiest to recognize. Hot water
from deep underground wells up to form hotsprings and geysers. This water
is laden with minerals, which precipitate out of it as the water cools.
Minerals with a high content of sulfur and arsenic are abundant in
hydrothermal areas, including several sulfur-based ores. These include
realgar, orpiment, raw sulfur, and sal ammoniac. Ores such as tenorite,
teallite, contunnite, selenide, bismite, millerite and cinnabar can be
found. Microcrystalline quartzes are also more common, such as agate, onyx,
sard, carnelian and sardonyx.
Karst geology is defined by the preponderence of lime-bearing minerals such
as limestone, dolostone and gypsum. Karst topography frequently has
pale-colored cliffs and caves abounding in exotic rock formations. Deposits
of carbonate minerals are more frequently found: flourite, calcite and
chalk, as well as carbonate ores like siderite, calamine, zinc spar,
cerussite and rhodochrosite. Substances such as petroleum and graphite tend
to be more common in karst geology as well. Flint is found in karst areas,
usually embedded in limestone. Experienced prospectors also report that
fossils are more abundant as well.
Lavas come in various sorts. Most are intermediate blends of iron-bearing
and silicate minerals. Some have more of one type or the other.
Felsic geology is made from lavas richer in silicates and alumina than
iron. The bed rock tends to be rhyolite, with granite deeper down or
exposed where non-plutonic minerals have weathered away. Crystalline
quartzes such as amethyst, citrine and smokey quartz can be found here.
Obsidian occurs in felsic geology, as do semi-precious stones such as
zircon, rutile and tourmaline. Ores are less common felsic regions.
Mafic geology is made from iron-rich lava. The bedrock tends to be darker
minerals such as basalt, hornblende and olivine. Semi-precious stones such
as scapolite, peridot, spinel, jade and diopside are more common. Ores such
as iron pyrite, hematite and manganite can also be found in mafic regions.
The rarest geological profiles are those found in dry alkaline lake beds
and salt flats. These arid environments are home to many rare halide and
nitrate minerals, including common table salt (halite), sylvite, anhydrite,
saltpeter, potash, bischofite, trona, bloedite, polyhalite and highly toxic
borax. While isolated deposits of these materials can sometimes be found in
deserts, there are only a handful of locations in the world that possess
them in abundance.
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