also called Sahara
a variety of Nuummite which
is an unapproved name for a metamorphic orthoamphibole
rock consisting primarily of two amphiboles - Anthophyllite and Gedrite.
Nuummite was discovered in Greenland in 1982 and was
only known to occur in Greenland until 2009 when a new
source of gem-quality iridescent orthoamphibole was
discovered in the Sahara Desert of central Mauritania.
samples of this new material were donated to GIA by
Scott Davies of American-Thai Trading in Bangkok. This
Nuummite from Mauritania has iridescence that is
mostly blue to bluish green, although some stones
show golden yellow and a small percentage are a highly
desirable pure blue. Unlike the original Greenland rocks,
the new Sahara Nuummite often has a high density of
needles, some of which can show a quite attractive blue
color. The blue color is said to be due to the presence
of titanium. The stones take a good polish, but cutting
the material is challenging as the colorful iridescent
needles only appear in very thin planes with a very
narrow viewing orientation in the rough making yields
spectra of the iridescent laths were consistent with
Anthophyllite and Gedrite, which are orthorhombic members
in the magnesium-iron-manganese-lithium amphibole group.
Testing confirmed that the flashy needles are in fact
the amphibole Anthophyllite, the main component of Nuummite.
The samples had RI measurements between 1.649 and 1.669,
consistent with the Raman identification. Hydrostatic
specific gravity was 2.98 ± 0.05, and the samples were
inert to long- and short-wave UV radiation.