Geosec Slides

Geosec Slides is run by Rob Gill from that hub of West Ardnamurchan small businesses, Achnaha.  Rob makes microscope slides of thin sections of rock, so thin that light can pass through them, which are used by geologists to study and identify their constituent minerals.

Rob starts the process by cutting rectangular pieces of the rock - seen at left - using a diamond cutting wheel.  These are then polished on one side, and that side is stuck down onto a glass microscope slide.  A machine then cuts the rock to a thickness of about 300 microns.

The slide is then mounted on an arm - seen at the left of this picture - which is dropped against the face of a fast-rotating diamond disk.  This thins the rock to between 100 and 150 microns.

What is remarkable about all the machines Rob uses to make the slides is that he built them himself.  Since they work to very small tolerances, this in itself is a remarkable achievement.

The last stages are done by hand.  Rob is seen here with the slide with the rock side face-down on glass grinding it using abrasive powders of steadily reducing grades.  The rock is by now extremely thin, and this part of the process requires both a skilled hand and a practised eye. The target thickness is 30 to 32 microns: for comparison a sheet of paper is about 100 microns thick.

The process is completed by gluing a glass cover over the rock section.  Some of the completed slides can be seen to Rob's left.

The slides are viewed through a polarising microscope.  As well as being able to see the slide through the eyepieces, the camera on top takes photographs which Rob uses to sell the slide.

This is the result.  Each mineral has characteristic colours and shapes - for example, the pale emerald green mineral at top right is olivine, the yellow/orange is pyroxene and the white/grey stripey mineral is feldspar.  This particular rock is local - it's taken from the great eucrite that forms part of the Ardnamurchan volcanic complex.

Rob advertises and sells his slides on ebay, and has customers all all over the world, with the US and Germany providing the majority of his clients.  In a few cases, customers send in the rocks they want made into a slide, but mostly Rob collects his own. So Rob travels extensively - rocks from Etna and Vesuvius are particularly popular - but he is fortunate that plenty of fine specimens can be found right here in West Ardnamurchan.

The Geosec Slides website, which includes a description of how the polarising microscope works, is here.