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Durangite

Discovered in 1869; IMA status: Valid (pre-IMA; Grandfathered)

Chemistry

Chemical Formula:

NaAl(AsO₄)F

Sodium Aluminum Arsenate Fluoride

Molecular Weight:

207.89 gm

Composition:

Sodium

11.06 %

Na

14.91 %

Na₂O

Aluminum

12.98 %

Al

24.52 %

Al₂O₃

Arsenic

36.04 %

As

55.28 %

As₂O₅

Oxygen

30.78 %

O

Fluorine

9.14 %

F

9.14 %

F

—    %

F

-3.85 %

-O=F₂

100.00 %

100.00 %

= TOTAL OXIDE

Classification

Mineral Classification:

Arsenates

Strunz 8th Ed. ID:

7/B.25-50

Nickel-Strunz 10th Ed. ID:

8.BH.10

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

Related to:

Tilasite Group. Forms two series; Durangite-Maxwellite Series and Durangite-Tilasite Series. Isostructural with Titanite.

Members of Group:

Tilasite Group: Isokite, Lacroixite, Maxwellite, Panasqueiraite, Tilasite.

Varieties:

None

Synonyms:

ICSD 30205, PDF 36-424

Crystal Data

Crystallography:

Monoclinic - Prismatic

Crystal Habit:

Typically in euhedral oblique pyramidal crystals, to 1 cm, slightly elongated along [001], with dominant {110}, {111}, and {010}, {100}, {021}, faces commonly dull and rough; in stacked aggregates. Artificial crystals are prismatic [101], and rarely tabular.

Twinning:

On {001} common as interopenetration twins (artificial crystals).

Physical Properties

Cleavage:

Distinct on [110]

Fracture:

Irregular/Uneven to Conchoidal

Tenacity:

Brittle

Moh's Hardness:

5.0 - 5.5

Density:

3.90 - 4.07 (g/cm³); Density is highest in dark-coloured, ferrian material.

Luminescence:

None

Radioactivity:

Not Radioactive

Optical Properties

Color:

Pale to dark red-orange, deep red, orange, orange-brown, pale yellow; in transmitted light, color zoned from varying contents of Fe and Mn. Green color exhibited by artificial material.

Transparency:

Transparent to Opaque

Luster:

Vitreous, usually dull

Refractive Index:

1.634 - 1.685  Biaxial ( - ) 

Birefringence:

0.051

Dispersion:

Strong, also weak to moderate; r < v, less commonly r > v 

Pleochroism:

X = yellow-orange; Y = pale yellow-orange; Z = nearly colorless.

Occurances

Geological Setting:

In veins in alkalic rhyolite and tin placers derived therefrom; in pegmatite dikes in granite.

Common Associations:

Cassiterite, Hematite, Topaz, Ilmenite, Tantalite, Wickmanite, Beudantite, Mimetite, Fluorite, Tridymite, Cristobalite, Quartz, Amblygonite, “Chalcedony”, Zeolites, clay minerals.

Common Impurities:

None

Type Locality:

Barranca Mine, Coneto de Comonfort, Mun. de Coneto de Comonfort, Durango, Mexico

Year Discovered:

1869

View mineral photos:

Durangite Mineral Photos and Locations

More Information

Mindat.org
Webmineral.com

Durangite is named for the type locality at the Barranca mine in the Durango state of Mexico. Durangite occurs in veins of alkalic rhyolite and tin placers that were derived from alkalic rhyolites and in pegmatite dikes through granite. Durangite is an extremely rare gem. Durangite crystals are found in colors of pale to dark red-orange, deep red, orange, orange-brown and pale yellow. The two most notable occurances for possible gem quality crystals are the Barranca tin mine, about 30 km northeast of Coneto de Comonfort, Durango, Mexico and in the Thomas Range, Juab County, Utah.

Other Durangite locations are near Lake Ramsey, New Ross, Nova Scotia, Canada; in tin prospects near Boiler Peak, in the Black Range, Sierra County, New Mexico, USA; at the Cheesewring quarry, Linkinhorne, Cornwall, England.

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