PHYSICAL PROPERTIES:
Chemistry: CaB3O4(OH)3-H2O
Composition: Hydrated Calcium Borate Hydroxide
Class: Carbonates
Subclass: Borates
Crystal system: monoclinic 2/m
Fracture:uneven
Hardness: 4.5
Specific gravity: 2.4
Luster: vitreous
Streak: white
Cleavage: perfect in one direction and
distinct in another
Color:white to clear.
Transparency: crystals are transparent to translucent
Associated Minerals: borax, calcite,
celestite, hydroboracite, kernite, ulexite and other borate minerals.
COMPOSITION:
Hydrous calcium borate (50.9% B203,
27.2% CaO, 21.9% H20).
The basic structure of colemanite contains endless
chains of interlocking BO2(OH) triangles and
BO3(OH) tetrahedrons with calcium, water molecules
and extra hydroxides interspersed between the chains.
DISTINGUISHING CHARACTERISTICS:
Resembles many other minerals, but its manner of occurrence
is a good guide. The blow- pipe test should prove its identity, as it
does not resemble many other borates.
ENVIRONMENT:
Colemanite, like other borates, is a complex mineral,
that is found in desert borax deposits and Tertiary clays in old lake
beds. Colemanite is a secondary mineral, meaning that it occurs after
the original deposition of other minerals. The mineral borax is directly
deposited in arid regions from the evaporation of water due to runoff
from nearby mountain ranges. The runoff is rich in the element boron
and is highly concentrated by evaporation in the arid climate. Ground
water flowing through the borax sediments is believed to react with
the borax and form other minerals such as ulexite. It is believed that
colemanite may have formed from ulexite. Colemanite is found in geodes
within the borax sediment. It's exact means of formation are still not
well understood.
CRYSTAL DESCRIPTION:
Crystals may be large well-formed bipyramidal and prismatic crystals.
The short prismatic habit is typical with good crystals that have complicated
faces. Equant crystals that appear stubby and bead like are also common.
The crystals are sometimes flattened and can appear bladed. The termination's
are either blunted or steeply pyramidal. Colemanite can also occur in
grainy aggregates, in massive form or as a drusy.
TESTS:
Blow pipe test, exfoliates (peels off) upon heating, so
violently that it is difficult to fuse on charcoal. Grain held in forceps
exfoliates but melts with protrusions a little like borax. Colors the
flame green. Soluble in hot hydrochloric acid, with the precipitation
of thin "snowflakes" of boric acid upon cooling.
LOCALITIES:
The largest deposits of this mineral are in the
southwestern U.S. Deposits such as Boron in Kern Co. Lang
in Los Angeles Co, Death Valley, the Frazier Mountain and
other California localities. Some of the largest crystals have come
from the Borax Pit #1, Death Valley, Inyo Co., California. Crystal filled
nodules associated with Celestine were found in the Calico district
in San Bernardino Co., California. Colemanite also comes from the Muddy
Mountains, Clark Co., Nevada. Localities outside the U.S. include the
Atacama Desert of Chile; Salinas Grandes, Argentina; Bigadic, Turkey;
and the Indebor Deposit, Kazakhstan.
USES:
Colemanite was the most important ore of borax until kernite was discovered
in 1926. Colemanite has many important uses. It is used in the manufacture
of heat resistant glass.
It is also used as a cleaning agent and has other industrial, medicinal,
and cosmetical uses.
FACTS & HISTORY:
Colemanite specimens in collections have a tendency to collect dust
in definite areas on crystal surfaces. Which might indicate that colemanite
is pyroelectric and develops an electrical charge during a change of
temperature. (Like tourmaline and quartz). The crystal symmetry of prismatic
monoclinic minerals would disqualify them from being pyroelectric, since
the effect is directly related to crystal symmetry. This mineral is
therefore regarded as a scientific oddity, and as of yet no explanation
has been given to how Colemanite is pyroelectric. Most specimens in
mineral cabinets show this conspicuous dustiness in special areas. It
is prevalent enough to be considered a distinguishing characteristic.
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