Pyrope

The mineral pyrope (from Greek pyropos = fiery ) is an island silicate from the garnet group, and has the chemical composition Mg3Al2 [ SiO4 ] 3

The mineral crystallizes in the cubic crystal system often ( rounded ) grains. In addition, in aggregates occurs. The color of pyrope varies from mostly black-red and blood red ( to pink), often with a brownish tinge.

Special Features

The pyrope is for example found in kimberlites. Therefore, it can be obtained as a byproduct of the degradation of diamond. Striking compared to other minerals is the relatively high hardness and the high specific weight.

Etymology and history

One of the earliest mentions of garnets as a gemstone in the Bible in the Book of Exodus, 28,18 as stone on the breastplate of the High Priest Aarron. Pliny the Elder summed up in his work Naturalis historia in book 35, chapter 25, a row of red minerals under the term Carbunculus together, including grenade. Further differentiation of this group into three subgroups ( ruby, spinel and garnet) was carried out by Albertus Magnus in 1250 in his work " De mineral linus et rebus metallicus ". The present name Pyrope is derived from the Greek " pyropos " = of fiery appearance, which alludes to the red color.

Classification

In the classification by Strunz, 9th edition of the pyrope falls under 9.AD.25, is thus an island silicates without additional anions; Cations in oktahedraler and usually greater coordination.

Varieties and modifications

Pyrope ( Mg3Al2 [ SiO4 ] 3) forms with Spessartine ( Mn3Al2 [ SiO4 ] 3) and almandine ( Fe3Al2 [ SiO4 ] 3) a mixed batch, the so-called " Pyralspit series".

Pyrope, spessartine and almandine occur rarely in pure form, but always contain a certain amount of iron, magnesium and / or manganese (sometimes a small proportion of yttrium).

Education and Locations

Pyrope is particularly found in ultramafic rocks such as serpentinites, peridotites and kimberlites, and secondarily in sands, gravels and soaps.

Most important occurrences of pyrope are in Europe in the Czech Republic ( Central Bohemian Massif ), in South Africa, especially in the vicinity of Kimberley and in Tanzania, Australia and the United States ( Arizona). Another important locality is situated in the village of Martiniana Po in Italy.

Crystal structure

Pyrope crystallized cubic space group Ia3d ( Raumgruppen-Nr. 230 ) with the lattice parameters a = 11.45 Å, and eight formula units per unit cell.

Use

Pyrope was especially prized during the 18th and 19th centuries as a gemstone ( " Bohemian garnet ").