Simpsonite

Discovered in 1938; IMA status: Valid (pre-IMA; Grandfathered)

Chemistry

Chemical Formula:

Al₄(Ta,Nb)₃O₁₃(OH)

Aluminum Tantalum Niobium Oxide Hydroxide

Molecular Weight:

813.65 gm

Composition:

Tantalum

53.37 %

Ta

65.17 %

Ta₂O₅

Niobium

5.71 %

Nb

8.17 %

Nb₂O₅

Aluminum

13.26 %

Al

25.06 %

Al₂O₃

Hydrogen

0.12 %

H

1.11 %

H₂O

Oxygen

27.53 %

O

100.00 %

99.51 %

= TOTAL OXIDE

Classification

Mineral Classification:

Oxides

Strunz 8th Ed. ID:

4/D.27-20

Nickel-Strunz 10th Ed. ID:

4.DC.10

4 : OXIDES (Hydroxides, V[5,6] vanadates, arsenites, antimonites, bismuthites, sulfites, selenites, tellurites, iodates)
D : Metal: Oxygen = 1:2 and similar
C : With medium-sized cations; sheets of edge-sharing octahedra

Related to:

None

Varieties:

None

Synonyms:

Calogerasite, ICSD 67673, PDF 15-705, Simpsonite (of Bowley)

Crystal Data

Crystallography:

Trigonal - Pyramidal

Crystal Habit:

Euhedral to subhedral crystals, tabular to short prismatic, with {1010} and {0001}, and rarely a few other forms, striated || [0001], to 2.4 cm; commonly in subparallel groups.

Twinning:

None

Physical Properties

Cleavage:

None observed

Fracture:

Conchoidal

Tenacity:

Brittle

Moh's Hardness:

7.0 - 7.5

Density:

6.68 -6.82 (g/cm³)

Luminescence:

Blue-white cathodoluminescence. May be fluorescent in SW UV; bright blue-white (Western Australia), bright pale yellow (Bikita, Zimbabwe), medium pale yellow (Ecuador), light blue (Paraiba, Brazil)

Radioactivity:

Not Radioactive

Optical Properties

Color:

Yellow, light brown, colorless, gray, yellow-brown when altered; colorless in transmitted light

Transparency:

Semitransparent, translucent

Luster:

Adamantine, vitreous, dull

Refractive Index:

2.045 - 2.025  Uniaxial ( - )

Birefringence:

0.020

Dispersion:

None

Pleochroism:

FNone

Occurances

Geological Setting:

An uncommon accessory mineral in some tantalum-rich granite pegmatites.

Common Associations:

Tantalite, Manganotantalite, Microlite, Tapiolite, Beryl, Spodumene, Montebrasite, Pollucite, Petalite, Eucryptite, Tourmaline, Muscovite, Quartz

Common Impurities:

None

Type Locality:

Tabba Tabba pegmatite, Wallareenya Station, Port Hedland Shire, Western Australia, Australia

Year Discovered:

1938

View mineral photos:

Simpsonite Mineral Photos and Locations

Unusual Gem Categories

Fluorescent Gems

More Information

Mindat.org
Webmineral.com

Simpsonite is an extremely rare gem that is very attractive in the bright yellow to yellow-orange colors. It is found in a few locations worldwide but only available in facetable crystals from Onça and Paraiba, Brazil and Tabba Tabba, Western Australia. Gems are usually very small since crystals are small and clean material is a very small percentage of the limited supply of Simsonite that has been found. Most crystals are completely opaque. It is a very durable gem with hardness of 7.5 and no cleavage. It would make a very attractive gem for jewelry if it was more abundant and available in larger sizes.

Simpsonite may exhibit fluorescence under shortwave UV light. The color of the fluorescence depends on the origin of the gem; bright blue-white (Western Australia), bright pale yellow (Bikita, Zimbabwe), medium pale yellow (Ecuador), light blue (Paraiba, Brazil). If you place your cursor over the picture above, you will see the light blue fluorescence of a Simpsonite gem from Paraiba, Brazil. Simpsonite may also exhibit blue-white cathodoluminescence.

Simpsonite was named in 1938 by Harry Bowley (1882-1958) in honor of Edward Sydney Simpson (1875-1939), government mineralogist and chemist of the Geological Survey of Western Australia. The Simpson Desert in Northern Territory, South Australia and Queensland in central Australia was also named for him. In 1897 he became mineralogist and assayer with the Geological Survey of Western Australia. He helped to establish the Western Australian School of Mines. Simpson was a founder of the Natural History and Science Society of Western Australia and its successor, the Royal Society of Western Australia which awarded him the Kelvin Medal in 1929. He was awarded the Clarke Medal by the Royal Society of New South Wales in 1934. Simpson published A Key to Mineral Groups, Species and Varieties in 1932 and a three-volume set Minerals of Western Australia was published after his death in 1939. Harry Bowley was appointed to succeed Simpson as Government Analyst in 1939. Bowley joined the Western Australian Geological Survey Laboratories in 1897, rising to become Director of the Western Australian Government Chemical Laboratories in 1946.

Simpsonite distribution: from Tabba Tabba, Western Australia. At the Alto do Giz pegmatite, near Parelhas, and the Onça mine, about 25 km distant, Rio Grande do Norte, Brazil. In the Al Hayat and Mdara mines, Bikita, and at the Benson No. 3 pegmatite, Mtoko, Zimbabwe. In Congo (Zaire), from Mumba, near Lake Kivu, Kivu Province, and in the Manono pegmatite, Katanga (Shaba) Province. At the Leshaia pegmatite, Vuoriyarvi carbonatite complex, Kola Peninsula, Russia. In Canada, from the Tanco pegmatite, Bernic Lake, Manitoba.

Simpsonite gems for sale: