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A

B

A and B are photo's of a scanned thin section of Essexite, taken in ordinary and cross-polarised light respectively. "The sample is from a dyke of porphyritic nepheline gabbro intruded into Ordovician wackes of the Southern Uplands Terrane (from B.G.S.)" Essexite was originally classified as a syenogabbro. The locality is Craighead Quarry (about NS919 239) between Crawfordjohn and Abingdon, Lanarkshire in Scotland. The large titanaugite phenocryst, near bottom left, is 6mm in length. Incidentally this rock was famous in Scotland for making curling stones.

Photo B shows that it is a coarse grained igneous rock consisting essentially of large euhedral clinopyroxenes of titanaugite, Ca(Mg,Fe,Ti)(Si,Al)₂O₆, a variety of augite rich in titanium and showing a bronze-brown colour in thin section, and olivines set in a matrix of plagioclase feldspar (labradorite, grey to white interference colours), nepheline and olivine. Here, the olivines tend to be rounded with bright interference colours, mainly yellows and blues. There are also opaques of magnetite or ilmenite.

C

D

C and D are photo's taken under the microscope. C is under plane polarised light. The olivines can be distinguished by their higher relief, e.g. near the centre. The opaque minerals are magnetite or ilmenite.

D is under cross polarised light. The cloudy matrix, e.g. at the top right hand, is mainly the feldspathoid nepheline. The feldspars show the typical "striped" plagioclase twinning (Carlsbad-albite twinning).

The photo to the left is of a polished section of essexite from Craighead Quarry (about NS919 239) between Crawfordjohn and Abingdon, Lanarkshire in Scotland.

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A	B
A and B are photo's of a scanned thin section of Essexite, taken in ordinary and cross-polarised light respectively. "The sample is from a dyke of porphyritic nepheline gabbro intruded into Ordovician wackes of the Southern Uplands Terrane (from B.G.S.)" Essexite was originally classified as a syenogabbro. The locality is Craighead Quarry (about NS919 239) between Crawfordjohn and Abingdon, Lanarkshire in Scotland. The large titanaugite phenocryst, near bottom left, is 6mm in length. Incidentally this rock was famous in Scotland for making curling stones.	Photo B shows that it is a coarse grained igneous rock consisting essentially of large euhedral clinopyroxenes of titanaugite, Ca(Mg,Fe,Ti)(Si,Al)₂O₆, a variety of augite rich in titanium and showing a bronze-brown colour in thin section, and olivines set in a matrix of plagioclase feldspar (labradorite, grey to white interference colours), nepheline and olivine. Here, the olivines tend to be rounded with bright interference colours, mainly yellows and blues. There are also opaques of magnetite or ilmenite.
C	D
C and D are photo's taken under the microscope. C is under plane polarised light. The olivines can be distinguished by their higher relief, e.g. near the centre. The opaque minerals are magnetite or ilmenite.	D is under cross polarised light. The cloudy matrix, e.g. at the top right hand, is mainly the feldspathoid nepheline. The feldspars show the typical "striped" plagioclase twinning (Carlsbad-albite twinning).
	The photo to the left is of a polished section of essexite from Craighead Quarry (about NS919 239) between Crawfordjohn and Abingdon, Lanarkshire in Scotland. Back to thin section thumbnails Top of page