Epidote

Epidote

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Minerals are compounds that we seem never to get enough of. Just when you think you know lots of minerals, another name pops up any you are back to square one. Minerals differ according to structure and complexity. While some are simple structured, others are more complex than you can imagine, and  Epidote being one of them.

 

The Epidote is a name derived from "epidosis", a Greek word meaning "addition." It is a mineral which has a complex structure with single SiO4 (i.e. single silicate tetrahedrons) and a double Si2O7. Epidote is a crystal with the chemical configuration of Ca2Al2 (Fe3+;Al)(SiO4)(Si2O7)O(OH) meaning that it is a calcium aluminium iron sorosilicate mineral. The chains in the structure are connected together by the silicate groups and ions. Given that they are parallel chains, the crystals develop a prismatic behaviour and their path of elongation are perpendicular to the symmetrical plane. Also, the colour (which can be grey, grey, black or brown), gravity and optical constants vary depending on the quantity of iron present in the mineral.

Epidote is regarded as a secondary rock-forming marble which occurs in schistose rocks that have a metamorphic origin. It can also be formed when minerals like feldspars, pyroxenes, micas and others which compose igneous rocks, are altered hydrothermally.

Other physical characteristics of the Epidote include:

It has a hard, shiny and transparent lustre which makes it look appealing. It has a monoclinic crystal system. It has an uneven fracture and is moderately hard. Along with its yellowish, greenish or brownish colour, it also has a streak which can be white or gray. The epidote can exhibit different forms, for example, in Untersulzbachthal; it is a brilliant green crystal with prismatic behaviour. In Alaska, it is a large green crystal in tube form and is usually dark.

The epidote is associated with other minerals like the andradite garnet, calcite, hornblende, the biotite and others.

 

Additional Resources

Elgin Marbles   Faux Marbling   Feldspar

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