Exposed surfaces of the Achlais amphibolite show a green-black colouration with a weak foliation developed, defined by white minerals (of uncertain composition). The foliation planes are separated by variable amounts of the white mineralisation.

Fresh surfaces of the amphibolite showed the grain size to be uniformly very fine grained with individual minerals being indistinguishable with the naked eye. The colour of the fresh surface was the same as the colour of the exposed surfaces additionally veins of calcite and occasional aggregates of pyrite are observed. The mineralogy is indistinguishable in hand specimen but contains a large proportion of mafic phases.

A thin section of the Achlais amphibolite was taken to assist in the comparison between this lithology and the Garbh amphibolite to test Park’s (op. cit.) hypothesis that it is the same unit as the Garbh amphibolite.

The thin section (figure 5) showed the grain size to be less than 0.025 millimetres with a well-developed "L" fabric shown by the alignment of minerals, and also shows kink folds affecting the lineation.

The mode of the rock was:

Amphibolite (hornblende) 70%, quartz 20%, iron ore opaques 5%, accessory calcite, epidote and chlorite.

Thus it is seen that the lithology found in the Achlais amphibolite is significantly different from that observed in the Garbh amphibolite and would therefore merit it’s distinction as a separate lithology from the Garbh amphibolite.

(Note: on later study the two units where found to be linked northwards at the hinge of a large Isoclinal fold. However, for the purposes of this mapping project, information outside the mapping area had to be discounted – thus are bred false impressions from undergraduate mapping projects)

No major structures where observed in the Achlais amphibolite although minor folding and lineations were observed (c.f. structural section).

The general orientation of the foliation surfaces was striking towards the Northwest - Southeast with very steep dips generally towards the Southwest (with a few dips to the Northeast).

The outcrop width is 385 metres.