Sample One

Sample Two

Knowle Quarry

The thin sections of the two samples from Andy Gray’s quarry (Knowle Quarry)

The two Knowle Quarry samples consist of the same rock type – a lamprophyric rock of minette type.  Small altered phenocrysts of pyroxene and biotite are set within an altered groundmass of K-feldspar, biotite and specular Fe(-Ti) oxide.  There are also carbonate- K-feldspar growths, which could represent either vesicle infills or an additional altered phenocryst phase (perhaps olivine).  One of the samples (the one that I have identified as ‘Knowle Quarry #2’) is more altered than the other and exists in a decarbonated state.  I attach a pair of microscope images (photomicrographs) showing the two stones in thin section; these are at the ‘same scale’.  Without going into great detail about what can be seen, note the areas of blue in the image of ‘Sample 2’ – these correspond to void space (now infilled by the blue-dye resin used during the sectioning process) and reflect the more altered, decarbonated state of ‘Sample 2’.

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