This specimen features several sprays of yofortierite to about 3 ½ mm with numerous small (ca ½ mm on edge) thick tabular orange crystals of eudialyte and a few fractured pseudomrphs of birnessite and ranciéite after sérandite to about 6 mm.
The specimen is a miarolitic cavity from near the top of the sill. Consequently it is somewhat weathered and a bit dirty. (But that’s why the birnessite/ranciéite is there.)
The first pair of photos (FOV 5.0 x 4.0 mm) shows perhaps the best of the yofortierite. It spans ca 3.6 mm. Individual fibers reach 1.6 mm.
The next pair of photos (FOV 5.5 x 4.2 mm) shows two more yofortierite sprays, the largest spanning ca 3.4 mm. Tabular eudialyte crystals can be seen along the bottom.
The fifth photo shows the best of the birnessite/ranciéite pseudomorphs. It is broken, but the morphology of the sérandite precursor is still evident.
The next to last photo (FOV 3 x 2 cm) is a macro close-up of the main part of the cavity.
As shown in the last photo, this is not a very “pretty” specimen. Found April 1998.
Regarding the IDs:
Eudialyte proper is the only “eudialyte group” mineral reported from this quarry. (There is a “mineral” somewhat similar to manganoeudialyte, but it it has not been possible to characterize it as a real mineral.) The color of eudialyte at the quarry ranges from “shocking” pink, to red, orange, etc. Color is irrelevant for identification here.
In general, it is not possible to visually distinguish yofotiertite from tuperssuatsiaite at this quarry. Until fairly recently, tupessuatsiaite was thought to be very rare here, so specimens of this sort were routinely labeled as yofortierite. However, it has recently been found that many of the lighter colored specimens from the sill are actually tuperssuatsiaite. Based on analysis of other specimens, I would still say that this sample is yofortierite. (The fibers may not look all that dark in the photos, but that is because, despite being fibrous, yofortierite has a “silky” luster and reflections make it look lighter.) But it has not been analyzed, so, strictly speaking, all I can claim is “palygorskite group”.
Information regarding the birnessite/ranciéte pseudomorphs is from László Horváth.
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