Saturday, May 4, 2013

very rare Musgravite or is it Taaffeite?


 Iwas unable to find allot of information on this  very rare gemstone.
The big question that poped up allot is  " Is it Musgravite or Taaffeite speical test must be used to tell these two gems about. 
If you are like me you love learn about Gemstones.

 In mineralogy, the name Musgravite refers to the mineral called Magnesiotaaffeite-6N’3S. It crystallizes in the trigonal system.

The closely-related Magnesiotaaffeite, which crystallizes in the hexagonal system, is known in mineralogy as Magnesiotaaffeite-2N’2S. Together, they are both part of the Taaffeite group.

Musgravite, described as a 'Rarity among the rare,' is a mineral, very similar to Taafeite in chemical composition.  

It is so rare that in 2005, there were only eight gem quality Musgravites in the world. Price per carat is around $35000.
The rare gems taaffeite and musgravite have lately become
more popular among collectors. Due to their similar chemical compositions
and crystal structures, their main gemmological properties overlap
and so sophisticated measurement techniques such as quantitative
chemical analysis, Raman spectroscopy or X-ray powder or single crystal
diffraction are needed for their identification. This study describes
an EDXRF instrument used as single-crystal X-ray diffraction apparatus
and the technique to identify taaffeite and musgravite in a relatively
conclusive procedure. A special rotating and tilting stage has been
constructed to non-destructively determine the differences in diffraction
pattern based on the different symmetries (trigonal and hexagonal),
unit cell dimensions and space groups of taaffeite and musgravite.
Taaffeite and musgravite from Sri
Lanka, Myanmar and Tanzania are rare
gemstones that are popular among
collectors  Gem-quality taaffeite and musgravite are both transparent,
commonly with red, purple, blue, violet, grey or very dark colours. Taaffeite
(BeMg3Al8O16) shows a wider range of colors (which are due to high amounts
of chromium and iron) than musgravite  (BeMg2Al6O12) which has only been
found as purplish grey, greenish grey, greyish blue, and dark stones to date.
These two mineral species, belonging to the same mineral group taaffeite, have
very similar chemical compositions and crystal structures and their gemmological
properties are so similar that they cannot be distinguished using standard
gemmological identification tests.

Musgravite is one of rare gemstones that have been sought these years for the collection at GAAJ laboratory. This gem material is known to be very difficult to be distinguished from taaffeite, which is also a rare variety, and its identification methods needed to be established. We were fortunate to obtain the samples that were said to be musgravite this time, and this, together with analysis on many pieces of taaffeite, lead us to a conclusion that both materials can be assuredly distinguished from each other.

  Musgravite is a silicate mineral whose main ingredients are beryllium (Be), magnesium (Mg) and aluminium (Al), and belongs to the same mineral group as taaffeite. Both gems had been thought polytype (crystals possessing layered structure; each of the structure is the
same but their cycle along the layering direction is different), however, from studies to date they are now assumed independent varieties that have different chemical composition and crystal structure.

  It was named ‘musgravite’after the area Musgrave in Australia from where the material was first found. The musgravite was later found also in Greenland and Madagascar, but neither of them produces gem quality material. Two pieces of faceted gem-quality musgravite from Sri Lanka were reported firstly in 1993. Several reports of identifying gem-quality musgravite followed that, but the number of identified musgravite only reaches to eight in total so far, and most of them are less than 1 carat in size. No one, to the author’s knowledge, was reportedly identified in Japan.

  One piece of the sample we obtained this time as a musgravite, together with 84 faceted pieces requested by our client to be identified as taaffeite or musgravite, were subjected to standard gemmological tests, UV-visible spectrophotometry and Raman spectral analysis, and 57 pieces of them were tested semi-quantitative chemical analysis by EDXRF. Two pieces of them were further tested by X-ray powder diffraction analysis. The results revealed that combination of UV-visible spectral analysis, Raman spectroscopy and semi-quantitative chemical analysis by EDXRF can identify musgravite non-destructively and accurately. The number of musgravite identified by our method this time was 11 pieces, including a piece of 4.5ct (the largest piece in the world to the author’s knowledge).

  Technical report on identification of musgravite and taaffeite was addressed at annual
meeting of the Gemmological Society of Japan in 2006 that was held at Kobe Design University on 22nd July.
Musgravite – $6,000/carat

Discovered in 1967 in the Musgrave mountains of Australia this gemstone occurs in a few colors, most notably green and violet.
It is likely that a small part of taaffeite on the market today is actually musgravite, as it is extremely hard to differentiate the two.
In the early 2000′s only a handful of cut gemstones existed. In the last few years it has been found in a number of other places, including Madagascar and Tanzania.
However, gemstone quality musgravite is still exceedingly rare. High quality greenish musgravite sells for $2,000-3,000 per carat, while violet stones are even more expensive at around $6,000 per carat.

If you one has more information on this rare gem please let me know. 
Thank you for viewing The Wonderful World of Gemstones"

1 comment:

  1. i have some gems that show similar colours as taafeite. they wer dmined by grandfather in 1980's and was kept aside. how to know if they are taafeites?