stocinis

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A

B

C

D

This specimen (A & B magn x50) was collected by one of our members, Mavis Gill, near Stocinis, East Harris, Outer Hebrides. (The web editor is entirely responsible for its interpretation). It is an amphibolite gneiss, i.e. a regionally metamorphosed rock composed of mainly hornblende and plagioclase feldspar. Amphibolites are formed by metamorphism of igneous rocks. The rock specimen itself shows gneissose banding in hand specimen, but here it is not very apparent. C & D are photo's taken with a scanner.

Photo A, plane polarised light, shows pleochroic brown/green hornblende, clear quartz and cloudy areas. Photo B shows the same view under x polars where the section is seen to consist of hornblende (typical cleavage can be seen on the left side), altered plagioclase feldspar (cloudy areas) and quartz, some of the latter showing "strain shadows", e.g. bottom left. Most of the feldspars have been heavily altered to compact aggregates of sericite, giving the cloudy appearance in A and the "speckled" appearance in B.

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A	B
C	D
This specimen (A & B magn x50) was collected by one of our members, Mavis Gill, near Stocinis, East Harris, Outer Hebrides. (The web editor is entirely responsible for its interpretation). It is an amphibolite gneiss, i.e. a regionally metamorphosed rock composed of mainly hornblende and plagioclase feldspar. Amphibolites are formed by metamorphism of igneous rocks. The rock specimen itself shows gneissose banding in hand specimen, but here it is not very apparent. C & D are photo's taken with a scanner.	Photo A, plane polarised light, shows pleochroic brown/green hornblende, clear quartz and cloudy areas. Photo B shows the same view under x polars where the section is seen to consist of hornblende (typical cleavage can be seen on the left side), altered plagioclase feldspar (cloudy areas) and quartz, some of the latter showing "strain shadows", e.g. bottom left. Most of the feldspars have been heavily altered to compact aggregates of sericite, giving the cloudy appearance in A and the "speckled" appearance in B.