Blue Colour-Change Gem Garnet from East Africa

Jobbins, E. A.; Saul, Julie Mather; Tresham, Anne E.; Young, Brent R.

doi:10.15506/jog.1975.14.5.201

Cited by 3 publications

(4 citation statements)

References 0 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Chemical analyses revealed a close correlation of RI (and SG) with the chemistry of colourchange garnets ( Figure 2). Previous studies on colour-change garnets (Jobbins et al, 1975;Stockton, 1985;Koivula, 1996a, 1996b;Johnson and Koivula, 1998b;Koivula and Kammerling, 1988;Schmetzer and Bernhardt, 1999) reported RI values between 1.757 and 1.770, a distinctly smaller range than that in the present sample selection. All samples remained inert when exposed to long and short-wave ultraviolet radiation.…”

Section: Physical Propertiescontrasting

confidence: 66%

“…daylight and incandescent light. Gem-quality garnets displaying colour change were first mentioned from East Africa (Crowningshield, 1970;Jobbins et al, 1975). In the following years similar garnets were further reported from Umba valley and Tunduru in Tanzania (Schmetzer and Ottemann, 1979;Schmetzer and Giibelin, 1980;Stockton, 1982;Hanni, 1983;Manson and Stockton, 1984;Stockton, 1985;Koivula and Kammerling, 1988) and from Athiliwewa and Embilipitiya in Sri Lanka (Johnson and Koivula, 1996b;Johnson and Koivula 1998a).…”

Section: Introductionmentioning

confidence: 93%

“…In the first detailed gemmological study of colour-change garnets from Madagascar, Schmetzer and Bernhardt (1999) separate colour-change garnets into two groups according to their chemistry. Most colourchange garnets are intermediate members of the pyrope-spessartine solid solution series containing minor amounts of vanadium a n d / o r chromium (Jobbins et al, 1975;Stockton, 1982;Manson and Stockton, 1984;Stockton and Manson, 1985;Koivula and Kammerling, 1988;Johnson and Koivula, 1996b;Johnson and Koivula, 1998b;Schmetzer and Bernhardt, 1999). All studied colour-change garnets from Madagascar belong to this group (Johnson and Koivula, 1998b;Schmetzer and Bernhardt, 1999).…”

Section: Introductionmentioning

confidence: 96%

See 2 more Smart Citations

New gemstone occurrences in the south-west of Madagascar

Milisenda¹,

Henn²,

Henn³

2001

Journ of Gemm

View full text Add to dashboard Cite

In late 1998, spectacular gemstone occurrences were discovered in the south-western part of Madagascar. The secondary deposits extend from the south of the Isalo National Park near the town of Ranohira up to the town of Sakahara further west with major mining areas around Ilakaka and south of Ankazoabo. The occurrences produce pink, blue, violet, yellow, orange, green, pale brown and colourless corundum varieties, spinels, chrysoberyls, garnets, aquamarines, tourmalines and other gems. Of particular importance are pink and blue sapphires which are found in large quantities. The gemmological properties of fancy-coloured sapphires correspond to those found in the Umba valley and Tunduru area in Tanzania whereas the blue sapphires are reminiscent of sapphires from Sri Lanka. In addition a number of pinkish-orange corundum varieties show colours and absorption spectra that correspond to Sri Lankan padparadschas. The geological environment of the new deposits in Madagascar is similar to the alluvial deposits of Sri Lanka and Tanzania and the three areas may have been part of single land mass before the break-up of Gondwana.

show abstract

Section: Physical Propertiescontrasting

confidence: 66%

Section: Introductionmentioning

confidence: 93%

Section: Introductionmentioning

confidence: 96%

See 1 more Smart Citation

New gemstone occurrences in the south-west of Madagascar

Milisenda¹,

Henn²,

Henn³

2001

Journ of Gemm

View full text Add to dashboard Cite

show abstract

“…Reports on colour-change gemstones are widespread in the gemmological literature (see e.g. Jobbins et al, 1975;Schmetzer and Gübelin, 1980a,b;Scarratt, 1980;Bosshart et al, 1982;Duroc-Danner, 1987;Bank andHenn, 1988, Dharmaratne, 1993;Federman, 1995). For the most part, these articles describe the gem material, and give an explanation of the features in the absorption spectrum that contribute to the colourchange behaviour.…”

Section: Introductionmentioning

confidence: 99%

Heat-treated Be-Mg-Al oxide (originally musgravite or taaffeite)

Schmetzer¹,

Bernhardt²,

Medenbach³

1999

Journ of Gemm

View full text Add to dashboard Cite

show abstract

Pyrope-Spessartine Garnets with Unusual Color Behavior

Manson¹,

Stockton²

1984

Gems & Gemology

View full text Add to dashboard Cite

T h e study of garnets by G I A J s Department of Research continues with a collection of 32garnets that display a varietyofh~ies and yet share a common tendency to show different colors under different sources ofligh t. Even when veryslight, the change of color is invariably greater than that enco~~ntered in other types of garnets. These unusual garnets proved to be composed principally of a variuble mjxture of pyrope (25-60 wt.Yo) andspessartine (20-56 wt. YO), with considerable almandine (2-1 7 wt.Yo) and grossulor (3-23 wt. YO) also present. Their primary chemical distinction lies in their V203+ Cr203 content, which is always in excess of 0.2 wt.Yo. In conjunction with their distinctive color behavior, these garnets m a y also be characterized on the basis of specific gravity and absorption spectrum.

show abstract

Blue Colour-Change Gem Garnet from East Africa

Cited by 3 publications

References 0 publications

New gemstone occurrences in the south-west of Madagascar

New gemstone occurrences in the south-west of Madagascar

Heat-treated Be-Mg-Al oxide (originally musgravite or taaffeite)

Pyrope-Spessartine Garnets with Unusual Color Behavior

Contact Info

Product

Resources

About