Altered granite in contact with schist
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Fact sheet
Description: 

Darwin wrote "Imperfect gneiss or mica slate at junction of granite & clay slate on Lion's Back. (Layers very thin; scales of mica small, layers slightly contorted; mica black, glittering; feldspar granular, yellowish; quartz in small quantity, very thin laminae, but perfectly characterized, mixed with coarse granitic veins, if indeed they are veins and not parallel layers)"

This section shows the contact of a biotite-rich schist (top left) with altered, coarsely-crystalline biotite granite. Large crystals of plagioclase feldspar are  partially replaced by sericitic mica. Quartz in the sample has been indurated with carborundum during sample preparation. Collected May-June 1836.

In Place
In Time
Location description: 
Cape Town, South Africa
Accuracy:
Location precision: 
Poor
Timescale:
Not known
Ma = Millions of years ago
In Focus
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Type:
Type: 
igneous
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