World-wide, leucosphenite is a very rare mineral. Judging from photos, by far the best crystals are those from MSH. But leucosphenite is also rare at MSH, where it is found almost exclusively in the igneous breccia and exceedingly rarely in marble xenoliths. This specimen is from one of these very rare marble xenolith occurrences. There are three sharply formed crystals/groups, one pale blue, the other two colorless. The largest leucosphenite crystal is about 2.25 mm tall.
One of the colorless leucosphenite groups is next to a very small (0.75 mm on edge) short-prismatic crystal of narsarsukite. Not only is the prismatic habit unusual, but the occurrence of narsarsukite in marble xenolith is also very rare.
The leucosphenite is associated with fairly well formed pectolity, and very snall, but also well-formed crystals of magnesio-arfvedsonite. The latter was analyzed on another specimen from this find. (The EDS scan is posted under the “Analysis” tab.)
The first pair of photos (FOV 3.35 x 2.45 mm) shows the colorless leucosphenite group that is associated with narsarsukite. The top leucosphenite crystal is 1.45 mm wide. As already mentioned, the “champagne” colored narsarsukite is ca 0.75 mm on edge. It may be hard to recognize this as narsarsukite – there is a “screw disclocation” at the top, resulting in spiral growth. But the overall cross-section is typical of MSH: octagonal with 4 long sides and 4 short sides.
The second pair of photos (FOV 4.7 x 3.85 mm) shows the pale blue group of leucosphenite crystals. The top crystal is 1.4 mm wide. The large crystal is 2.2 mm tall. This group is hard to spot, even with the arrow that I have provided. (The yellow arrow shown in the full view fell off. There are now three red arrows, each pointing to one of the leucosphenites.) Although the habits are distinctly different, at first glance, leucosphenite and pectolite can look very similar. Some of the pectolite even has a pale blueish tinge.
The third pair of photos (FOV 3.3 x 2.4 mm) shows the other colorless leucosphenite crystal. It is 2.25 mm long. It too is hard to spot, because it is tucked in a tight crevice between pectolite crystals.
The fourth pair of photos (FOV 4.4 x 6.75 mm) shows one of the larger, terminated, pectolite crystals on the specimen. In front are several smaller, well-terminated, pectolite crystals. The small dark green (zoned) prisms are magnesio-arfvedsonite.
The narsarsukitel is easy to overlook and I probably would not have recognized it as narsarsukite, were it not for two larger (more prismatic) crystals/aggregates found on other specimens. That’s all I found – three crystals/groups. But by the time I got there, there was not much of this material left, so no doubt other specimens exist – perhaps unrecognized. Even the larger crystals are easy to miss. In any case, this is a most unusual specimen. It is also the only one that I have which has both leucosphenite and narsarsukite.
Single item shipping weight (w TN case) is 3.4 oz (96 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).
