15 research outputs found
New data on painite
A crystal of painite discovered in 1979 in a
parcel of rough gem spinel from Burma represents the
third known crystal of the species. This crystal is similar to
the type crystal in most respects. Chemical analyses of
both the new crystal and the type crystal confirmed the
essential constituents reported by Moore and Araki
(1976) and showed in addition the presence of trace
amounts of Fe, Cr, V, Ti, Na, and Hf. Optical absorption
spectra suggest that the red colour of painite is caused
principally by Cr^(3+) and V^(3+)
Upper Stage Engine Composite Nozzle Extensions
Carbon-carbon (C-C) composite nozzle extensions are of interest for use on a variety of launch vehicle upper stage engines and in-space propulsion systems. The C-C nozzle extension technology and test capabilities being developed are intended to support National Aeronautics and Space Administration (NASA) and United States Air Force (USAF) requirements, as well as broader industry needs. Recent and on-going efforts at the Marshall Space Flight Center (MSFC) are aimed at both (a) further developing the technology and databases for nozzle extensions fabricated from specific CC materials, and (b) developing and demonstrating low-cost capabilities for testing composite nozzle extensions. At present, materials development work is concentrating on developing a database for lyocell-based C-C that can be used for upper stage engine nozzle extension design, modeling, and analysis efforts. Lyocell-based C-C behaves in a manner similar to rayon-based CC, but does not have the environmental issues associated with the use of rayon. Future work will also further investigate technology and database gaps and needs for more-established polyacrylonitrile- (PAN-) based C-C's. As a low-cost means of being able to rapidly test and screen nozzle extension materials and structures, MSFC has recently established and demonstrated a test rig at MSFC's Test Stand (TS) 115 for testing subscale nozzle extensions with 3.5-inch inside diameters at the attachment plane. Test durations of up to 120 seconds have been demonstrated using oxygen/hydrogen propellants. Other propellant combinations, including the use of hydrocarbon fuels, can be used if desired. Another test capability being developed will allow the testing of larger nozzle extensions (13.5- inch inside diameters at the attachment plane) in environments more similar to those of actual oxygen/hydrogen upper stage engines. Two C-C nozzle extensions (one lyocell-based, one PAN-based) have been fabricated for testing with the larger-scale facility
Green orthoclase feldspar from Vietnam
In July 2005,
these contributors received some interesting transparent
"emerald" green samples that were reported to be amazonite
from a new find in Vietnam. Five faceted stones
were loaned and several pieces of rough were donated to
GIA by Bill Larson (Pala International, Fallbrook,
California). According to his supplier, Son T. Ta (I.T.C.
International Trade Center, Ho Chi Minh City, Vietnam),
they were mined from a pegmatite near Minh Tien, about
15 km south of Luc Yen in Yen Bai Province. This area is
also known to produce transparent green fluorite, which
when cobbed is similar in appearance to gem-quality
orthoclase
Origin of color in cuprian elbaite from São José de Batalha, Paraíba, Brazil
Gem-quality elbaite from Paraíba, Brazil, containing up to 1.4 wt% Cu has been characterized using optical spectroscopy and crystal chemistry. The optical absorption spectra of Cu^(2+) in these tourmalines consist of two bands with maxima in the 695- to 940-nm region that are more intense in the E ⊥ c direction. The vivid yellowish green to bluegreen colors of these elbaite samples arise primarily from Cu^(2+) and are modified to violetblue
and violet hues by increasing absorptions from Mn^(3+)
New data on Lotharmeyerite
The new species lotharmeyerite from the Ojuela mine, Mapimi,
Durango, Mexico was recently described by Dunn (1983). Unfortunately,
the very small crystals in drusy growths which that author
had at his disposal did not permit the determination of a number of
important characteristics. The availability of larger, individual
crystals from the same locality now makes possible a more complete
description of the species
Causes of the purple and pink colours of manganoan sugilites from the Wessels Mine, South Africa
Gem-Quality Cuprian-Elbaite Tourmalines from São José Da Batalha, Paraíba, Brazil
Unusually vivid tourmalines from the state of Paraíba, in northeastern Brazil, have attracted great interest since they first appeared on the international gem market in 1989. This article describes what is known of the locality at this time, but focuses on the most striking characteristic of these gem tourmalines: the unusual colors in which they occur. Quantitative chemical analyses revealed
that these elbaite tourmalines contain surprisingly high concentrations of copper, up to 1.92 wt.% Cu (or 2.38 wt.% CuO). Their colors are due to Cu^(2+) or a combination
of Cu^(2+), Mn^(3+), and other causes. Some colors can be produced by heat treatment, but most also occur naturally
Developments in Gemstone Analysis Techniques and Instrumentation During the 2000s
The first decade of the 2000s continued the trend of using more powerful analytical instruments
to solve gem identification problems. Advances in gem treatment and synthesis technology, and
the discovery of new gem sources, led to urgent needs in gem identification. These, in turn, led to
the adaptation of newer scientific instruments to gemology. The past decade witnessed the
widespread use of chemical microanalysis techniques such as LA-ICP-MS and LIBS, luminescence
spectroscopy (particularly photoluminescence), real-time fluorescence and X-ray imaging,
and portable spectrometers, as well as the introduction of nanoscale analysis. Innovations in laser
mapping and computer modeling of diamond rough and faceted stone appearance changed the
way gemstones are cut and the manner in which they are graded by gem laboratories