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Donnayite-(Y) With Pyrite On Dolomite


Donnayite-(Y) With Pyrite On Dolomite


Description Tabs

Poudrette Quarry, Mont Saint-Hilaire, Québec, Canada
Crystals on Matrix
Size Range: 
Cabinet (10-18 cm)
5.5 × 10.5 × 7 cm

This is a fairly large specimen from a hornfels seam with lots of good dolomite crystals and pyrite. But the real interest here is the blue-gray “donnayite” shown in the close-up photos. This stuff is somewhat lumpy but relatively abundant on the specimen.

According to qualitative EDS (see the “Analysis” tab) on an another specimen from a similar,near-by, find, the donnayite is mixed in with FeSO4 and/or pyrite. It is typical at MSH for donnayite to be sprinkled with and to include pyrite. It isn't clear just from EDS whether any or all of the Fe and S is coming from such pyrite, or if (at least some of) the pyrite has altered to an FeSO4 mineral. The "donnayite" on this specimen has less visible pyrite on it, so perhaps it would have produced a purer donnayite EDS scan. 

The first two photos (FOV 6.9 x 4.5 mm and FOV 6.7 x 4.5 mm resp.) are slightly different views  shows the most heavily “donnayite” populate area – and a relatively large, but rather twinned, pyrite crystal, plus a couple of small dolomite crystals.

The third photo (FOV 4.9 x 6.9 mm) shows a few more “donnayite thingies” and dolomite crystals. The dolomite crystals are sharply formed and translucent, but they are encrusted by oxidized pyrite which does make them look dirty.

The fourth photo (FOV 6.9 x 4.5 mm) shows another typical dolomite crystal 2.6 mm on edge with a few of the more attractive pyrite cubes on the specimen. There are one or two larger cubes, but most of the pyrite is heavily twinned.

In addition to the “donnayite” crystals shown in the photos, there are several similar crystals/blobs sparsely scattered over the specimen.

Note: The “dolomite” is a visual ID. Possibly there is an epitactic crust of another carbonate on top of dolomite. Ankerite epitactic on siderite is known from the carbonate pegmatites at MSH, but I don’t think that’s what this stuff is. In any case – not analyzed.

Found 5/98 a hornfels seam near the Poudrette pegmatite

This is a heavy item. It is probably not possible to trim it without destroying it. Single item shipping weight is 18.2 oz (515 g). Note that USPS foreign packet rates recently increased significantly. If you wish to hold an "open box" so as to reduce postage costs by combining items from a future auction, let me know and I will generate a new, “item only”, invoice with postage TBD at the time of actual shipment.

Outside the USA, the stated postage and packing rate applies up to a total weight of 32 oz (900 g).

Within the USA, I will use Priority Mail. Up to 32 oz, the “own box” Priority rate is $13.00 (including packing).

Please see my "Shipping Policy" for details. 

Mineral Data
What's on the rock


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: 
6.0 - 6.5


Crystal System: 
Trigonal - Rhombohedral
3.5 - 4.0
Analysis Report - only: Donnayite-(Y) With Pyrite On Dolomite
LMB minerals

Seller Information

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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.