Description

Large, hematoidal, partially chloritic quartz crystal from the Bierghes quarry in Walloon Brabant, 30 km west of Brussels. These quarries have been exploiting “porphyry”, a plutonic magmatic rock, since the 18th century, first for church construction and then for ballast production due to its good mechanical and chemical properties. The operation frequently encountered metric cracks of excellent quality quartz crystals reminiscent of Alpine facies (developed prism, Dauphiné habitus). However, these quartz are much older than alpine quartz, dating back 300 million years to the Hercynian orogeny.
The magazine “Le Règne Minéral” devoted an article to this quarry on the occasion of an exceptional discovery of decimetric quartz plates.

Video of this Bierghes quartz specimen :

This post is also available in: French