MSH is the TL for steacyte. It is a rare mineral here and very rare world-wide. Brown cruciform twins, characteristic of MSH, are probably the best know. There are several other, very uncommon, habits here. But the closely packed, radiating, habit on this specimen is unique in my experience. (Radiating spays of – colorless! - steacyite are known from Água de Pau, but not from MSH.) It was a great surprise when EDS said “steacyite”. (See the “Analysis” tab).
For MSH, this is a truly remarkable specimen – once you realize what you are looking at. Moreover, the steacyite is associated with eudidymite (or perhaps epididymite), which may also be a unique association. (The “eudidymite” was analyzed via EDS, but it is not possible to distinguish eudidymite from epididymite in this way. I am calling it eudidymite based on habit. But this one of those ambiguous cases. I can’t guarantee that it is not epididymite.)
The first pair of photos (FOV 1.4 x 1.75 mm) shows one of the two main steacyte aggregates. These are very small crystals, the diameters are < 0.05 mm, and, in this view, the entire aggegate spans < 1.5 mm. My scope doesn’t really have sufficient resolution for such small objects, so the photo is rather blurry. But I think that you can see that the radiating prisms have square cross-sections (with a somewhat uneven “rind”). You will need 50-60X to see the crystals as in the photos. (But through a scope they will probably look better than in the photos.)
The second pair of photos (FOV 2.25 x 2.8 mm) shows the same aggregate at lower magnification. Some of the eu/epidymite is visible on the left.
The third pair of photo (FOV 1.75 x 1.35 mm) shows the other main steacyite aggregate. These crystals have more of a cream color and the aggregate is more “open”.
The next pair of photos (4.4 x 6.2 mm) shows the largest of the eu/epididymite groups. It spans about 4.5 mm. Individual laths are ca 3.2 mm long. One of the radiating steacyte aggregates can be seen at top center. It spans about 1 mm in this view.
Regarding the IDs: Bear in mind that these are qualitative EDS scans, made with equipment that cannot “see” anything lighter than Na, e.g. Be. (Very low energy peaks of other elements are also not detected.) Na is detected only weakly and Si is detected much less readily than Th, K and Ca. Allowing for all that, both the steacyite and eu/epididymite scans are good matches.
Single item shipping weight (with MIN case) is 3.1 oz (88 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 increases by about $0.20 per ounce. Above 13 oz, I will use Priority Mail (approx $9.25 including packing).
