ClassicGems.net

Amblygonite

Discovered in 1818;   IMA status: Valid (pre-IMA; Grandfathered)

Chemistry

Chemical Formula:

LiAl(PO₄)(F,OH)

Lithium Aluminum Phosphate Fluoride Hydroxide

Molecular Weight:

151.41 gm

Composition:

Sodium

3.80 %

Na

5.12 %

Na₂O

Lithium

3.44 %

Li

7.40 %

Li₂O

Aluminum

17.82 %

Al

33.67 %

Al₂O₃

Phosphorus

20.46 %

P

46.88 %

P₂O₅

Hydrogen

0.17 %

H

1.49 %

H₂O

Oxygen

44.91 %

O

Fluorine

9.41 %

F

9.41 %

F

—  %

F

—3.96 %

—O=F₂

100.00 %

100.00 %

= TOTAL OXIDE

Classification

Mineral Classification:

Phosphates

Strunz 8th Ed. ID:

7/B.02-30

Nickel-Strunz 10th Ed. ID:

8.BB.05

8 : PHOSPHATES, ARSENATES, VANADATES
B : Phosphates, etc., with additional anions, without H₂O
B : With only medium-sized cations, (OH, etc.):RO₄ about 1:1

Related to:

Amblygonite Group. Griphite-Tavorite Series.

Members of Group:

Amblygonite Group: Amblygonite, Montebrasite, Natramblygonite, Natromontebrasite, Tavorite

Varieties:

Hebronite

Synonyms:

None

Crystal Data

Crystallography:

Triclinic - Pinacoidal

Crystal Habit:

Crude crystals, typically equant with complex form development, to 1.5 m; massive.

Twinning:

On several laws, with microscopic polysynthetic twinning common.

Physical Properties

Cleavage:

[100] Perfect, [110] Good, [011] Distinct

Fracture:

Irregular/Uneven, Sub-Conchoidal

Tenacity:

Brittle

Moh's Hardness:

5.5 - 6.0

Density:

3.04- 3.11 (g/cm³)

Luminescence:

None

Radioactivity:

Not Radioactive

Optical Properties

Color:

Milk-white, yellowish, beige, salmon-pink, greenish, bluish, grey

Transparency:

Transparent, Translucent

Luster:

Vitreous to Greasy, Pearly on good cleavages

Refractive Index:

1.578 - 1.613  Biaxial ( - )

Birefringence:

0.020 - 0.030

Dispersion:

r > v

Pleochroism:

None

Occurances

Geological Setting:

An uncommon accessory mineral in zoned granite pegmatites; in high-temperature tin veins and greisens.

Common Associations:

Lacroixite, Apatite, Lithiophilite, Spodumene, Lepidolite, Petalite, Pollucite, Tourmaline (pegmatites); Cassiterite, Topaz, Mica (greisens).

Common Impurities:

None

Type Locality:

Chursdorf, Penig, Chemnitz, Saxony, Germany

Year Discovered:

1818

View mineral photos:

Amblygonite Mineral Photos and Locations

More Information

Mindat.org
Webmineral.com

Amblygonite is a beautiful gem usually pale straw yellow. Darker, more saturated "lemon" yellow gems are rarer and more highly prized. An extremely rare lilic colored Amblygonite comes from Karibib, Namibia. Amblygonite is very closely related to Montebrasite and varies only by optiacal property. Amblygonite is optically (-) and Montebrasite is optically (+). It may be that if many Amblygonite gems where retested, they may actually be Montebrasites. In general, it is thought that most yellow gems on the market are Amblygonite, and most colorless gems are Montebrasite, but this does not always hold true.

The name Amblygonite is from the Greek words ambly for blunt and goni for angle, referring to the fact that its cleavage angle slightly differs from 90°, distinguishing it from Scapolite for which it was originally mistaken.

The few localities for analyzed material include: from Chursdorf and Arnsdorf, near Penig, Saxony, Germany. On Utö Island, near Stockholm, Sweden. In the USA, at Hebron, Oxford County, Maine; large crystals in San Domingo Wash, northeast of Wickenburg, Maricopa County, Arizona. From the Tanco pegmatite, Bernic Lake, Manitoba, Canada. At Coolgardie, Western Australia. From near Karibib, Namibia. In the Muiâne pegmatite, Alto Ligonha district, Mozambique.

Amblygonite gems for sale: