MSH is the TL for gaidonnayite. It is moderately uncommon in general, but was locally abundant in some parts of the Poudrette pegmatite. This specimen is, instead, from a hornfels breccia, probably unrelated to that pegmatite. Unlike most MSH gaidonnayite, which fluoresces bright green, these crystals have essentially no UV response. More importantly, the crystals from this find are relatively simple and untwined – the orthorhombic symmetry is clearly evident. The crystals are glassy, have a somewhat unusual blue-gray color, and are translucent and even partly transparent. However, small pyrite crystals encrust most of the crystals to some degree.
The first pair of photos (FOV 3.7 x 2.3 mm) shows the best crystal, which is twinned on the bottom, but is essentially a very fine single crystal on the top. Altogether it spans 1.6 mm. The longest edge on the top face is 1.0 mm. There is an aggregate of smaller, darker, crystals on the right. These are well-formed, but more heavily twinned. They can be seen more clearly in the second pair of photos (FOV 6.6 x 4.2 mm), which is a broader view of the same area. The large, pyrite encrusted aggregate on the right in these photos, is more gaidonnayite, but it cannot be seen clearly. The prismatic crystal above this may be apatite, but is also encrusted and the form can’t be seen clearly. Epididymite, fairly large crystals of which were found on other specimens, might be another possibility. The brightly lit crystal on the left is a small, but almost perfect single crystal of gaidonnayite.
The gaidonnayite is accompanied by a carpet of small white needles of fluorapatite. The apatite was analyzed via EDS in order to eliminate other possibilities. (EDS cannot determine that it is fluoraptite, but, apart from “carbonate fluoraptite”, which is just a variety, fluorapatite is the only “apatite” currently on the MSH species list. See the “Analysis” tab.)
In the background are sharply formed crystals of dolomite and possibly another carbonate. There are two distinct habits: pseudo-octahedral and thin tabular (similar in habit to the flattened rhodochrosite crystals that MSH is known for). The tabular crystals are pale yellowish, the “octahedral” crystals are pale blue-gray or white and partly translucent. I don’t know if these are just two different generations of dolomite, or two distinct carbonates. Dolomite, siderite, and etc. generally have intermediate compositions at MSH and it is not really possible to identify specific species without analysis. In many cases, the interior and exterior of a crystal may be a different carbonate.
Single item shipping weight is 2.8 oz (79 g). For shipments outside the USA, up to a total weight < 8 oz (225g), this can be combined with items from this or other auctions for the same postage.
Within the USA, postage now varies by destination. For total weights up to 13 oz, it ranges from $4.50 to $7.00 (including packing etc). Above 13 oz (up to 16 oz), I will use “own box” Priority Mail. The rate, including packing, varies from $8 to $10.