Mineral of the Month - Barite
February 22, 2011
Barite
from Rosh Pinah, Namibia. ± 20 cm X 13
cm X 13 cm Specimen and
photos – J de Jongh
Crystal
system: Orthorhombic Hardness: 2,5 - 3,5
Density: 4.5 average Cleavage: very good
Streak: white
Colour: Colourless,
white, blue, red, yellow, orange, pink, purple, brown gray, black and
green.
May also be
multi-coloured and banded.
Occurrence: It most often occurs in
hydrothermal veins, lead-zinc veins in limestones and with hematite ore.
Habitat: It is usually
found as colourless or massive mineral, but may form prismatic or tabular
crystals as well as fibrous masses and granular aggregates.
Composition: sulfate
BaSO4
There is a well-known song of which the lyrics go something like “He
ain’t heavy he’s my brother”. The
mineral of the month, however, is in fact very heavy and it is my barite.
The barite group consists of barite, celestine, anglesite and
anhydrite. Barite itself is generally
white or colourless, and is the main source of barium. The name barite is derived from the Greek
word “baryos” meaning heavy. It fluoresces in a variety of colours and
sometimes it is also phosphorescent.
Barite is the main ore of the element barium. It is used in the manufacturing of paints,
paper and rubber and also as added-value applications which include the motor
industry, electronics, TV screens, etc. Also as radiation shielding and medical applications (for example, a
barium meal before a contrast CAT scan). When crushed, it is added to mud to form barium mud, which is poured
into an oil well during drilling. These high density muds are circulated down
the drill stem and returned to the surface between the drill stem and the wall
of the well. The action effectively
flushes the cuttings produced by the drill and carries them to the surface.
Historically barite was used for the production of barium hydroxide for
sugar refining and as white pigment for textiles and paint.
Although barite contains a “heavy” metal, it is not considered to be a
toxic chemical by most governments because of its extreme insolubility.
Barite is well-known for its great range of colours and varied crystals
forms. It is an immensely popular
mineral among collectors. Barite is
easily identified by its heavy weight, since most similar minerals are much
lighter. It often replaces other
minerals, and may even replace organic materials such as wood, shells and
fossils. It sometimes even forms mounds
from deposition of hot, barium-rich springs. It has also been identified in meteorites.
Barite specimens from certain localities are brown from sand inclusions
and may occur in beautiful rosette aggregates that strikingly resemble a
flower. These are known as barite
“desert roses”. The mineral gypsum also
forms similar desert roses, but they are much lighter in weight, and are more
brittle and thin.
Barite is a very common mineral and is found in thousands of localities
in too many countries to mention. Southern Africa localities include South Africa, Namibia, Zimbabwe, Botswana,
and Swaziland.
The largest barite crystals in the world came from the Elandsrand gold mine near Carletonville in Gauteng. These attractive, amber-coloured crystals were discovered in 1997 in a cavity 2600 m below the surface, associated with quartz, galena, carbon and pyrite. The largest known crystal from this locality and, therefore, most probably also in the world, is 70 cm x 30 cm and weighs 64 kg and is on display in the mine office. A picture of this huge crystal can be seen on page 45 of Bruce Cairncross’s book, “Field Guide to Rocks & Minerals of Southern Africa”. Barite has also been found in other Witwatersrand gold mines such as the Kopanong mine.
Barite is also relatively common mineral in the Kalahari manganese
fields. The barite is white or colourless, but may be pale yellow. Finds of large barite crystals up to 16 cm
long have been reported from the Wessels mine.
The famous Tsumeb mine also produced chocolate-brown tabular crystals,
some up to 10 cm long.
In my opinion the premier locality for aesthetic barite crystals are
strangely enough not from either of the latter two world famous localities, but
from the Rosh Pinah mine in the Luderitz district, 20 km north of the Orange
River, Namibia. The sulfate deposit has
been mined since 1969. The colour of the
best specimens is a rich golden orange and large crystals over 4 cm long are arranged in
radiating sprays up to 30 cm
in diameter and were found in 1989. Some
“floater” specimens are composed of complete 3600 discs resembling
Aztec suns. The finest specimens have
the barites crystals on matrix - JDJ.
References
Cairncross, Bruce,
(2004) – Field Guide to Rocks & Minerals of Southern Africa.
Cairncross, Bruce,
(1997) – The Manganese Adventure.
Posted by Site Moderator Webmaster. Posted In : Mineral of the Month
