Rhomb Porphyry

Rhomb Porphyry
Rhomb Porphyry Rhomb Porphyry 3" Specimen with Cut and Lacquered Face
Rhomb Porphyry
Excl. Tax: £1.00 Incl. Tax: £1.20

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An igneous rock exhibiting a porphyritic texture containing large cubic crystals of feldspar within a fine grained matrix. Collected near Oslo, Norway. Each sample is supplied in a labelled card tray. Each sample is supplied in a labelled card tray.

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Excl. Tax: £1.00 Incl. Tax: £1.20
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Rhomb porphyry is an porphyritic alkaline syenite composed of an alkali feldspar groundmass with augites having rhombohedral cross sections as the principal phenocryst minerals. It is formed when a column of rising magma is cooled in two stages. The first deep in the crust creating the larger crystals with a diameter of 2mm or more. In the final stage at much shallower depths or during ejection from a volcano the cooling is rapid creating the much finer matrix. Traditionally the term "Porphyry" refers to the purple- red form of this stone prized in antiquity for it's hardness & excellent building qualities particularly in Ancient Rome. This rock specimen is available in various optional sizes as well as in a 3" size piece with a cut and lacquered face to detail the crystal structure of the rock in much clearer detail.
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