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Gaidonnayite On Dolomite With Fluorapatite


Gaidonnayite On Dolomite With Fluorapatite

Type Locality

Description Tabs

Poudrette Quarry, Mont Saint-Hilaire, Québec, Canada
Crystals on Matrix
Size Range: 
Thumbnail (1-3cm)
1.2 × 1.1 × 0.9 cm

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.

Mineral Data
What's on the rock


Crystal System: 
5.0 - 0.0
Type Locality: 
Poudrette quarry (Demix quarry; Uni-Mix quarry; Desourdy quarry; Carrière Mont Saint-Hilaire), Mont Saint-Hilaire, La Vallée-du-Richelieu RCM, Montérégie, Québec, Canada


Crystal System: 
Trigonal - Rhombohedral
3.5 - 4.0


Crystal System: 
Type Locality: 
Sauberg Mine, Ehrenfriedersdorf, Erzgebirge, Saxony, Germany
Analysis Report - only: Gaidonnayite On Dolomite With Fluorapatite

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Start 08 Mar 18:00
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Seller's terms and conditions

In addition to the standard terms and conditions, please note the following. Almost all IDs are visual. While in most cases the ID is obvious, there may be cases where it is not. If you are doubtful about a particular ID, please ask for more information. Or do not bid! Similarly, if you are not sure that the specimen meets your criteria, do not bid. I have tdone the best I can with the photos. Nevertheless, if you are not happy with a specimen for any reason, I will refund the bid price – but not the shipping costs (unless the fault is clearly mine) – if the specimen is returned. This policy applies even if analysis of the specimen shows that my ID was incorrect. When in doubt, ask - or don’t bid. Note that most crystals at MSH and Varennes are micros - even if on large specimens. Please pay attention to the stated sizes. Any customs duties, fees etc. are the responsibility of the buyer.

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