Shomiokite-(Y) is a very rare mineral at MSH. This is a significant example. Encrusting the shomiokite-(Y) is adamsite-(Y), another very rare mineral, for which MSH is the TL.
According to Pekov (“Lovezero Massif”), at its type, and only other, locality, the “Shomiokitovoe pegmatite” in the Umbozero mine , shomiokite-(Y) formed up to 40-50% of the core of the pegmatite, and the initial mass reached perhaps 10 tons. So, worldwide, it is hard to claim that shomiokite-(Y) is a rare mineral. Yet, even from Umbozero, specimens are not plentiful.
According to Pekov, shomiokite crystals at Umbozero can be much larger than the ones found at MSH, but most are shattered due to post-emplacement changes in the environment (in particular hydration-dehydration). Consequently, terminated crystals are very rare.
At MSH, shomiokite-(Y) frequently grows in open cavities, but terminated crystals are still uncommon , not only because of hydration-dehydration, but because of the small size of the cavities, which results in crystals running into each other and/or the walls – hence no terminations. Shomiokite-(Y) is also fairly brittle, resulting in breakage when collecting specimens.
Moreover, at MSH, shomiokite-(Y) commonly alters to, or is encrusted by, adamsite-(Y). That is the case on this specimen, but, as shown in the first pair of photos (FOV 6.9 x 4.3 mm), several of the crystals have distinct pinacoidal terminations despite the adamsite coating. The visible portion of the long crystal at the bottom of these photos is 6.6 mm. Its total length is about 8-9 mm. (But the bottom is hidden by other crystals so it is impossible to be sure how far the “root” goes.)
On the far right of these photos is a small (1.2 mm) franconite aggregate which caps a shomiokite crystal growing nearly straight out of the photos.
The next pair of photos (FOV 4.5 x 6.8 mm) shows the franconite aggregate again and provides a clearer view of the shomiokite crystals, some of which are also terminated, growing beneath the franconite. (But the “pedestal” crystal on which it grows is only partly visible.)
Altogether, the shomiokite-(Y) spans about 10 x 11 mm. Fairly strong REE absorption lines can be seen. The radiating green prisms are aegirine. The reddish grains are rhodochrosite.
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