MSH is known for exceptional specimens of narsarsukite. Crystals up to 5 cm have been reported, but most crystals are much smaller - the largest I ever found was about 1 cm. However. it is the smaller crystals that have the most interesting habits and which are the most attractive.
The crystals on this specimen are at most 1.3 mm, which is smaller than average. But the habits are extremely unusual – so unusual that even when I got my first EDS results, I had trouble understanding how this could be narsarsukite. Thinking I had sent the wrong sample, the scan was repeated with another sample which produced the same result. Being forced to look at the crystals as “narsarsukite” I began to recognize a few forms, but I will make no attempt to interpret the habits shown in any of the photos. (For diagrams of narsarsukite habits reported from MSH, see the Lapis or Rivista Mineralogica special issues on MSH from 2000. Few, if any, of the diagrams are obvious matches for the crystals on this specimen.)
In addition to the narsarsukite, there are also several crystals of colorless leucosphenite (also confirmed via EDS), and nice prisms of an amphibole which, according to the EDS scan, miught fall into the “Richterite Root Name” family. This specimen is from the Poudrette pegmatite complex, but given the “breccia like” mineral assemblage, “richterite” would not be unexpected.
There are four known “richterite” species at MSH: richterite, ferro-richterite, fluoro-richterite, and potassic-richterite. None of the end members of these species is a good match for the EDS scan of this specimen, because the end members have either MG or Fe – not both. Something intermediate between ferro-richterite (Fe) and potassic-richterite (Mg, K), might be plausible. However, a qualitative EDS scan is far from sufficient to identify specific amphiboles. Even “Richterite Root Name” is just a tentative hypothesis. Note: e-Rocks does not currently accept “Richterite Root Name” so I had to resort to calling it “Richterite Amphibole”!
All of these crystals grew in a very narrow seam in (brecciated?) hornfels, and consequently some are contacted.
The first 6 photos show some of the narsarsukite crystals. They are all very sharply formed and gemmy, but many have interrupted growth due to the “richterite”. The FOV is, respectively, 1.75 x 1.4 mm, 1.95 x 1.3 mm, 1.9 x 1.3 mm, 1.3 x 1.65 mm,1.85 x 1.3 mm, and 2.2 x 2.4 mm. Crystal sizes are 0.5 – 1.3 mm. You will need 20-50X to view these crystals clearly. Some crystals are twinned and many are parts of larger groups, which makes deciphering the morphology more difficult.
The next three photos show some of the leucosphenite. These crystals have habits that are fairly typical for MSH. The FOV is, respectively, 3.25 x 2.3 mm, 3.05 x 2.2 mm, and 1.15 x 1.75 mm.
There are other narsarsukite and leucosphenite crystals on the specimen, but parts of the “richterite” prisms show up in almost every photo.
Single item (no case) shipping weight is 7.9 oz. Within the USA, the shipping cost for additional items is about $0.20 per ounce. Above 13 oz, I will use "own box" Priority Mail. The cost is about $9.25 up to 16 oz - varies by destination.
For shipments outside the USA, additional items will push the shipping cost into the next band. The extra cost is ca $6 to $9.50, depending on destination. This rate is good up to 32 oz (1.9 kg).