They are important minerals in sediments, evaporate deposits and low
temperature hydrothermal veins.
They react to HCl, and their anion is CO.
the most common
carbonate mineral. It is a calcium carbonate and it forms many
different types of crystals such as rhombohedral, scalenohedral,
butterfly twin, dog-tooth, nail-head and Iceland spar. It can also be
stalactitic, fibrous, granular or massive. It can be colourless, white,
brown, grey, red, green or black.
Dolomite by Paul via Flickr.com
is the second commonest carbonate mineral. It is a calcium magnesium
carbonate and it can form rhombohedral or tabular crystals; or be
granular or massive. It can be white, colourless, pink, grey or brown.
It forms in magnesium limestones,
magnesium rich metamorphic
rocks, and in hydrothermal veins, associated with copper,
zinc and lead ores.
Siderite. By Jan Helebrant via Flickr.com
commonest carbonate mineral. It is an iron carbonate, and it can form
prismatic, tabular, scalenohedral or rhombohedral crystals. It can also
be granular or massive. It is a widespread mineral and can be found in
as well as hydrothermal veins.
is a calcium carbonate which chemical formula is identical to calcite.
It forms in oxidised conditions and while white or colourless when
pure, it can be coloured reddish, brownish, yellowish, greenish, blue
or purple by impurities. It is more unstable than calcite and can alter
to calcite. It forms orthorhombic crystals or can be radiating,
fibrous, stalactitic, columnar or coral-like.
Rhodochrosite by Eric Hunt via Flickr.com
is a beautiful
pink mineral, although it can also be grey or brown. It is a manganese
carbonate and can form tabular, prismatic, scalenohedral or
rhombohedral crystals, or be botryoidal, nodular, globular,
stalactitic, granular or massive. It forms in hydrothermal veins, and
sedimentary and metamorphic deposits.
Magnesite. By James St. John via Flickr.com
carbonate which forms rhombohedral crystals but most often is granular,
fibrous, lamellar or massive. It can be white, colourless, brownish,
yellowish or grey. It forms by alteration in magnesium rich rocks, or
as a primary mineral in some schists
It is used as a source of magnesium.
Smithsonite. By Orbital Joe via Flickr.com
is a zinc
carbonate. It is most often found in stalactitic or botryoidal habits,
but rarely forms large crystals. It may be white, blue, grey, green,
yellow, brown, pink or purple. It is found in oxidation zones of zinc
deposits assocated with hemimorphite, polymorphite, azurite and
malachite. It is mined as a zinc ore.
Ankerite, Black Country Museums via Flickr.com
carbonate that forms rhombohedral crystals that are similar to
dolomite's. It can also be granular or massive. It is most often brown
but can also be white, colourless, yellowishn or grey. It forms in
mineral veins in dolomite (rock) and limestone. It can be associated
Azurite is a
blue copper carbonate. It can form prismatic crystals or be earthy,
botryoidal, stalactitic, nodular or massive. It is formed in oxidised
zones of copper deposits when carbonated water acts on copper minerals.
It is often associated with malachite. It is mined as a copper ore, but
has historically also been used as a pigment.
carbonate, which has been one of the earliest ores of copper. It can
form acicular or prismatic crystals, or be fibrous, stalactitic or
bortyoidal. It has a beautiful deep green colour and has been
extensively used in buildings and jewelry. It forms in oxidised copper
zones and is often associated with azurite.