64 pages, full colour.

The late Neil Yedlin, whose micromounting column in The Mineralogical Record may be familiar to older readers, would exhort collectors to buy and use a good mineral book, advice which remains as good today as it did thirty years ago. It also provides the subject of this editorial in a rather oblique manner, borrowing the words ‘buy and use’ to which is added (with an ironic flourish as Yedlin was a supreme micromounter) ‘a good stereomicroscope’. Modern stereomicroscopes provide superb optical quality and in relative terms they are less expensive than at any time in history. In other areas of microscopy, complex specimen preparation is the norm, but a stereomicroscope simply requires the user to sit down at a bench and look. Specimens are revealed in breathtaking detail, opening up a whole new world…

Assembling a mineral collection usually involves both scientific and aesthetic decisions. Why else would factors such as rarity and damage be so important? There is no single item of equipment that is more useful when investigating the scientific and aesthetic qualities of a specimen. A stereomicroscope invites closer investigation, and this almost automatically leads to a deeper understanding of mineralogy.

Occasionally collectors take the view that stereomicroscopes are purely for those who collect micromounts. Nothing could be further from the truth! It’s hard to imagine a collector who wouldn’t benefit from investigating his or her specimens using a stereomicroscope. Unusual assemblages and crystal morphologies are revealed, rare species and associations can be investigated, and any attempts at fakery are quickly apparent. The number of completely new species which have been discovered in this way is considerable: the mineral ‘scrutinyite’ even records the process formally in a name, which alludes to the careful investigation of the specimen that was required to find and characterise it.

Many collectors are content simply to use their microscope for visual observation, but with the addition of a few accessories it can do much more. It is relatively easy, for example, to do a variety of micro-chemical tests. The simple chemical tests for copper, lead and carbonate minerals should be part of every mineralogist’s toolkit. Add polarising filters and simple optical investigations become possible. These almost inevitably lead into the chemistry and physics of minerals and the process of scientific investigation.

Improvements in manufacturing technique and lens design in the last two decades together with the competition brought about by manufacture in the Far East have made good quality stereomicroscopes relatively cheap. The rise in the expectations of the semiconductor and biotechnology industries has produced considerable improvements in capabilities of high-end instruments and these have fed into the collector market. A good stereomicroscope can be purchased new for less than a thousand pounds and a second-hand instrument (if it is well looked after) for perhaps a little over half the new price. The author recently purchased a small, light stereomicroscope to take on field trips for a little under £50 (second-hand), it produces a crisp image at a single magnification of 20x and cost about the same as the petrol required to pick it up.

Twenty five years ago the cost of a good stereomicroscope was perhaps five to ten times that of a ‘fine British mineral specimen’, today they are about equal. In relative terms, microscopes, like cameras, computers and other manufactured goods, have become less expensive and more capable. You get an awful lot of bang for your buck! So at the conclusion to this piece I would strongly recommend any reader who does not already have one to buy and use a good stereomicroscope. It will add immeasurably to your enjoyment of mineralogy.

Primary lead and copper sulphide mineralisation is present in quartz-barite veins in Ordovician mudstone rocks of the Skiddaw Group at Saddleback Old Mine in the upper Glenderamackin valley, Mungrisdale, Cumbria. At the shaft dump, a sparse supergene assemblage comprising brochantite, caledonite, cerussite, chenite, connellite, cuprite, goethite, leadhillite, mimetite, malachite, pyromorphite and pseudomalachite has developed in cavities near partially oxidised lead and copper sulphides. In cavities that are spatially separated from the sulphides, pyromorphite and pseudomalachite are the dominant supergene minerals, the latter occasionally occurring in rich micro-crystalline crusts.

About 100 m upstream from the shaft dump a vein crops out in the river bank. Lead mineralisation is conspicuous at this point and it displays the commonly observed galena-cerussite-pyromorphite oxidation sequence.

At the head of the Glenderamackin valley, about half a kilometre beyond the mine site, manganese-rich quartz veins (containing lithiophorite and hollandite) host small quantities of supergene lead mineralisation. Hinsdalite and corkite pseudomorphs after pyromorphite are abundant and plumbogummite and plumbojarosite are also present.

An examination of the supergene mineralisation suggests that the leaching of copper and lead into the environment is buffered by phosphate. The stable and insoluble phosphates pyromorphite and pseudomalachite predominate at the shaft dump and a well defined galena-cerussite-pyromorphite oxidation sequence has developed at the nearby vein exposure. The supergene lead mineralisation at the head of the valley is dominated by another phosphate, hinsdalite. These assemblages probably reflect enhanced phosphate concentrations in the Skiddaw Group sediments.

The rare manganese oxide hydroxide mineral feitknechtite has been discovered intergrown with hausmannite in material collected from Benallt manganese mine during its last phase of working in the 1940s. The Benallt material is identical to the mixture ‘hydrohausmannite’ described from Franklin, New Jersey, U.S.A., and Långban and Pajsberg, Värmland, Sweden. This is the first record of feitknechtite in the British Isles. It occurs in massive manganese ore which also contains either iwakiite or jacobsite, rhodochrosite, caryopilite, fluorapatite and pennantite.

Several distinct mineral assemblages are present on the dumps of North Devon United Mine, Peter Tavy, Devon. The mine, which lies within the metamorphic aureole of the Dartmoor Granite, is of special scientific interest because of its complex and diverse ore mineralogy. Tin-tungsten-arsenic mineralisation in vein quartz is almost certainly part of the high temperature mineralisation which occurs in east-west trending veins throughout Cornwall and Devon. Scheelite, rather than the more usual wolframite, is the primary tungsten-bearing mineral. A complex polymetallic chlorite-dominated assemblage contains a wide variety of lead, copper, zinc and bismuth bearing minerals including the first British parkerite and ikunolite. It has considerable mineralogical affinities with the polymetallic chlorite lodes that are present at shallow levels in many mines at or near the margins of granitic bodies in Cornwall.