A |
Photo A is from a thin section of a coarse
grained granite taken with crossed polars. It is a classical example
of an alkali granite, viz. where the feldspars are mainly potassic
consisting of orthoclase and microcline. The granite was found on the
beach near the ferry terminal of North Uist, grid ref. NF 923 812. It
is probably a glacial erratic.
The biotite crystal in photo A, near bottom
left, its interference colours masked by its natural brown colour, is
1.5mm in length. |
B |
C is a photo of the thin
section taken with a scanner and using crossed polars, hence the grey
and white interference colours of the feldspars and quartz. The
biotite micas, light to dark brown colours, average 1.5mm in length. |