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Sandy BraesAntrim
Sandy Braes, Co.Antrim, May 1997.
Summary Full report
Site Type: Quarry (disused)
Site Status: ASSI
District:
Grid Reference: J32063958
Rocks
Rock Age: Tertiary
Rock Name: Antrim Lava Group
Rock Type: Agglomerate, Obsidian, Perlite
Interest
Minerals: Opal, Quartz, Sanidine
Other interest: No data, No Data

Summary of site:

Sandy Braes was a volcanic centre of extreme violence during the Palaeocene, around 65 million years ago (see Sandy Braes, site 517). The local rhyolitic lavas were derived from the basaltic lavas that dominated the Antrim Plateau and had evolved into viscous, quartz-rich rocks. Some of these lavas chilled to form a natural glass called obsidian and crystals of sanidine (potassium aluminium silicate), a high temperature form of a common feldspar mineral (orthoclase), are suspended in this fine-grained matrix. Orange-red opal is also found in tiny veins permeating these rocks, most likely to have been formed when hot springs, saturated in dissolved silica, were a common feature of the volcanic landscape.


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