Axinite-(Fe)  (Ferro-Axinite)
Current inventory:  0 gems
 

  
Axinite-(Fe) is named from the Greek word acine meaning ax in allusion to the acute shape of typical crystals. The modifier Ferro is from the Latin word ferrum meaning "iron" in reference to the Fe in the chemical formula.

Discovered in 1909;  IMA status: Valid (pre-IMA; Grandfathered)

Chemistry

Chemical Formula:

Ca₂Fe²⁺Al₂(BO₃)Si₄O₁₂(OH)

Calcium Iron Aluminum Boron Sorosilicate Hydroxide

Molecular Weight:

570.12 gm

Composition:

Calcium

14.06 %

Ca

19.67 %

CaO

Aluminum

9.47 %

Al

17.88 %

Al₂O₃

Iron

9.80 %

Fe

12.60 %

FeO

Silicon

19.71 %

Si

42.16 %

SiO₂

Boron

1.90 %

B

6.11 %

B₂O₃

Hydrogen

0.18 %

H

1.58 %

H₂O

Oxygen

44.90 %

O

100.00 %

100.00 %

= TOTAL OXIDE

Classification

Mineral Classification:

Silicates (Germanates)

Strunz 8th Ed. ID:

8/E.06-10

Nickel-Strunz 10th Ed. ID:

9.BD.20

9 : SILICATES (Germanates)
B : Sorosilicates
D : Si₂O₇ groups, with additional anions; cations in tetrahedral [4] and greater coordination

Related to:

Axinite Group. Axinite-(Fe)-Axinite-(Mg) Series. Iron analog of Axinite-(Mg) and Axinite-(Mn)

Members of Group:

Axinite Group: Axinite-(Fe), Axinite-(Mg), Axinite-(Mn), Tinzenite

Varieties:

Feraxinite, Ferro-Axinite

Synonyms:

None

Crystal Data

Crystallography:

Triclinic - Pinacoidal

Crystal Habit:

Crystals typically flattened, axe-head-shaped, to 20 cm; granular, massive.

Twinning:

None

Physical Properties

Cleavage:

Distinct on {100}, Poor on {001} and {110}

Fracture:

Irregular/Uneven to Conchoidal

Tenacity:

Brittle

Moh's Hardness:

6.5 - 7.0

Density:

3.25 - 3.28 (g/cm³)

Luminescence:

None

Radioactivity:

Not Radioactive

Optical Properties

Color:

Brown, Purplish blue, Gray, Greenish yellow

Transparency:

Transparent to Subtransparent

Luster:

Vitreous (Glassy)

Refractive Index:

1.672 - 1.701  Biaxial ( - )

Birefringence:

0.0090 - 0.0110

Dispersion:

Strong, r < v

Pleochroism:

X = colorless, yellow, light brown, yellow brown, or pale green; Y = colorless, deep yellow, deep blue, pale violet, or violet; Z = colorless, pale green, olive yellow, brown, or dark violet

Occurances

Geological Setting:

In low- to high-grade regionally metamorphosed rocks, in contact metamorphosed rocks, and in pegmatites.

Common Associations:

Epidote, Tremolite, Calcite (London Bridge, Australia); Prehnite, Epidote, Actinolite, Vesuvianite (Luning, Nevada, USA)

Common Impurities:

n/a

Type Locality:

St. Christophe-en-Oisans, Bourg d'Oisans, Isère, Rhône-Alpes, France

Year Discovered:

1909

View mineral photos:

Axinite-(Fe) Mineral Photos and Locations

More Information

Mindat.org
Webmineral.com

Axinite-(Fe) is a somewhat rare gem and is usually intensely trichroic with brown and purple colors being dominant. Axinite-(Fe) is the iron analog of Axinite-(Mg) which is the Magnesium analog. It is difficult to find material without internal flaws and feathers. Despite the inclusions, Axinite is a magnificent gem because of its rich colors and brilliance.

There are many localities for Axinite-(Fe), even for fine crystals. On Roscommon Cliff and in the Botallack mine, St. Just, Cornwall, England. From Bourg d'Oisans, Isère, France. In the Maderantal, Uri, Switzerland. Extraordinary crystals from the Puiva deposit, about 100 km west-northwest of Saranpaul, Subpolar Ural Mountains; at Zlatoust, Ural Mountains; and elsewhere in Russia. At Skardu, Pakistan. In the Obira mine, Bungo, Oita Prefecture; the Toroku mine, Miyazaki Prefecture; and elsewhere in Japan. In the USA, from Coarse Gold, Madera County, near Yreka, Siskiyou County, and New Melones Lake, Calaveras County, California; and from Elkhorn, Jefferson County, Montana. In Canada, found near Hope, British Columbia, and in the Moneta mine, Timmins, Ontario. From Trinidad, Baja California, Mexico. At Vitoria da Conquista, Bahia, Brazil.
 

  
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