West Cornwall - Geology
Elvan Dyke / Rhyolite - Praa Sands - 2 (S21)
At the western end of Praa Sands in Sydney Cove is an exposure (20m wide strip) of red brown Rhyolite (Elvan) ,
a quartz-feldspar-porphyry.
Intruded as a magma (molten rock) through a vertical crack in the earths crust 270 million years ago ,
the very viscous magma crystallised as Rhyolite with Feldspar phenocrysts (crystals).
The Crystals exhibit a well developed - similar orientation (Flow Texture).
The surrounding rocks are dark Mudstones .
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Location - Praa Sands is between St Michael's Mount and Porthleven - section 21
Ref: 188C
Date: 21/09/2014
Location: SW 573 280