Baryte and Marcasite

Baryte

It generally occurs as tabular and prismatic crystals, but also in sandy rosette aggregates (the so-called Desert Roses) and in granular, fibrous and lamellar aggregates. It is generally colourless, but there is no lack of examples of white, grey, yellowish, brown, reddish, bluish or greenish baryte. Transparent to translucent, it has a vitreous, resinous or pearly lustre. The characteristics that make it easily recognisable are its insolubility, the absence of effervescence in acids, its high specific gravity and its cleavage into parallelepiped forms.

It originates in hydrothermal veins, in clay nodules and in the cavities of sedimentary rocks.

It is used for the extraction of barium salts. Ground, it is used as a pigment, and finally, barium sulphate is used in medicine for certain X-ray examinations.

Marcasite

The crystals formed by this mineral are often prismatic and elongated, stubby or tabular. Cerussite is sometimes found in compact, granular and stalactitic masses. Although it is generally white or colourless, some specimens, owing to the presence of inclusions such as galena, show a grey, greenish or blue colouring. It is soluble in nitric acid, giving rise to violent effervescence.

It forms in the oxidised surface zones of deposits rich in lead minerals, then becoming associated with other alteration minerals.

It is used for the extraction of lead, and secondarily also of silver. Given the beauty of some specimens, its use is sometimes purely for collecting or scientific purposes.