Cancrisilite is a very rare mineral, reported only from MSH and five localities in the Kola Peninsula. This is an excellent example, with numerous small crystals to ca 2 mm. The cancrisilite is associated with rinkite/mosandrite. Both species were confirmed via EDS – see the “Analysis” tab.
Regarding the cancrisilite ID: I am not sure if EDS by itself is sufficient to distinguish cancrisilite from cancrinite, but the scan is a good match for what one would expect for cancrisilite. In addition, all of the pale violet/lilac and colorless “cancrinite” from MSH that has been rigorously analyzed has apparently been found to be cancrisilite. Only the (massive) yellow stuff is cancrinite. (See Mindat.)
Regarding the rinkite/mosandrite ID: Rinkite vs mosanmdrite has a long and convoluted history at MSH. Currently, both rinkite-(Ce) ((Ca3REE)Na(NaCa)Ti(Si2O7)2(OF)F2) and mosandrite-(Ce) ((Ca3REE)[(H2O)2Ca0.5☐0.5]Ti(Si2O7)2(OH)2(H2O)2) are on the MSH species list. The analyst suggested “mosandriite” as the best fit for the EDS scan. But going by the formulae, it would seem that the only difference between rinkite-(Ce) and mosandrite-(Ce) that might be apparent via EDS, would be the presence or absence of Na. Based on that, rinkite-(Ce) would be more likely in this case However, the equipment used is very insensitive to Na, so it could just be “hiding” in the noise. To be safe, I have labeled the tan needles as “rinkite group” (“rinkite” for short).
The first photo (FOV 3.5 x 2.3 mm) shows numerous small, very pale lilac, cancrisilite crystals. The largest one in this photo is ca 1.0 mm long.
The next pair of photos (FOV 5.4 x 4.2 mm) shows a cancrisilite aggregate ca 1.7 mm in diameter, surrounded by smaller, more prismatic cancrisilite crystals and tan needles of “rinkite” to ca 1.5 mm.
The next photo (FOV 3.65 x 2.5 mm) is a close-up of the central aggregate shown in the previous pair of photos. A smaller, radiating, aggregate can be seen on the left. A close-up of this radiating aggregate is shown in the next photo (FOV 1.4 x 2.0 mm). It seems a bit strange to have two such distinct habits of cancrisilite “cheek-by-jowl”), but the color and luster are identical to that of the more equant crystals.
The next pair of photos (FOV 2.3 x 2.8 mm) shows the largest cancrisilite crystal on the specimen. It may actually be two crystals stacked one on top of the other. On the left side the “join” is so smooth that it appears like a single crystal 2.0 mm tall. But on the right side, the upper is crystal is smaller, resulting in an offset – not a break – on that side. This may be clearer from the next two photos (FOV 2.35 x 3.0 and 2.3 x 2.65 mm resp.) The “cap” crystal is about 0.8 x 0.5 mm. The lower crystal is 1.8 mm wide. It is not developed on all sides. The back is attached to more cancrisilite behind this crystal.
Single item shipping weight is 3.2 oz (91 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 ($9.25 including packing).
