This strongly layered rock is also strongly altered and microcrystalline enough for minerals to be indistinguishable. The layering is defined by alternating dark and light lenses. Frequently, elongated, flattened vesicles will have a lighter-colored rim. This thin section has a greasy-looking film on the surface that makes it difficult to focus clearly.
A continuous foliation defined by aligned euhedral biotite characterizes this fine-grained sample. Granoblastic quartz and feldspars fill the voids between biotite crystals. Small, equant opaqes are distributed evenly throughout.
Like KRB10, plagioclase and clinopyroxene are intergrown in an almost graphic texture, though where KRB10 was dominated by the unknown mineral, in KRB11, that unknown mineral is confined to spherulite-like clusters in a fine-grained quartz matrix. Iddingsite alteration is much less extensive. Western Minerals Inc. as an 'interstitial ferrotholeiite, very highly fractionatedâ€¦textures are similar to those associated with rapidly frozen or highly viscous melts.'
The unknown mineral is the prominent mineral in this thin section. It forms a dusty brown, isotropic matrix with a faint dendritic texture in which subhedral clinopyroxene and plagioclase grains are set. Clinopyroxene, where isolated, is strongly altered to iddingsite. The degree of alteration is much lower where plagioclase and clinopyroxene grains are intergrown. The two minerals have an almost graphic intergrowth texture. Western Minerals Inc. as an 'interstitial ferrotholeiite, very highly fractionatedâ€¦textures are similar to those associated with rapidly frozen or highly viscous melts.'
This fine grained sample is fairly monomineralic. The small, feathery crystals are aligned to form a weak foliation. Opaques are plentiful though sphene much less so.
This sample is an almost monomineralic hornblende amphibolite with trace occurances of poikiloblastic orthoclase and biotite. Biotite growth concentrates along the margins of a high relief, clear mineral with fifth-order birefringence, extreme enough that the inclusions appear to not go extinct. Rarely are radiaiton halos observed in hornblende crystals.
The hornblende crystals in this thin section are prismatic and subhedral to euhedral in shape. They are strongly aligned. Filling in between the amphiboles are altered feldspars, granular epidote crystals and euhedral apatites.
Described by Western Minerals Inc. as 'porphyroblastic metasediments/hybrid rocks, interpreted by Eales and his coworkers as metamorphosed 'Red Beds' Formation sediments but conceivably magmatic in origin. The specimens illustrate the range in textures and compositions.' If so, textures in this sample, though difficult to describe, better resemble those of igneous than sedimentary rocks. This sample is jumbled mess of bladed, graphically intergrown k-feldspar and clinopyroxene, subhedral plagioclase altering to a dendritic, cloudy mineral, patches of anhedral, granular quartz, and elongate, poikilitic opaques.