Axinite: The mineral axinite information and pictures

About

Axinite is the group name for several closely related minerals: Axinite-(Fe), Axinite-(Mg), Axinite-(Mn), and Tinzenite. Axinite on its own without a sub-designation is not recognized as an individual mineral species by the IMA, although many mineral collectors still refer to it by its traditional name without further classifying the type of Axinite. Most of the known Axinite minerals are of the Axinite-(Fe) type.

Axinite was named in 1787 after the Greek word axine, which means "ax", in allusion to the sharp crystals of this mineral. The individual member types were originally Ferro-axinite, Magnesio-axinite, and Mangan-axinite. These were renamed with a suffix designation for easier cataloging reference by the IMA in 2008.

Identification

Chemical Formula: The inclusive formula for Axinite, encompassing all members, is:
(Ca_,Fe,Mg,Mn)₃Al₂BSi₄O₁₅(OH)

Individual members are:
Axinite-(Fe): Ca₂FeAl₂BSi₄O₁₅(OH)
Axinite-(Mg): Ca₂MgAl₂BSi₄O₁₅(OH)
Axinite-(Mn): Ca₂MnAl₂BSi₄O₁₅(OH)
Tinzenite: (Ca,Mn)₂MnAl₂BSi₄O₁₅(OH)
Composition: Basic aluminum boro-silicate of calcium, iron, magnesium, and manganese
Color: Smoky brown, dark brown, purplish-brown, greenish-brown, gray, black. Less commonly purple, blue, green, orange, or yellow. Very rarely multicolored. Axinite is strongly dichroic.
Streak: Colorless
Hardness: 6.5–7
Crystal System: Triclinic
Luster: Vitreous
Cleavage: 2,1
Fracture: Conchoidal to uneven
Tenacity: Brittle
Transparency: Transparent to nearly opaque
Specific Gravity: 3.3–3.4
Group: Silicates; Cyclosilicates
Rock Type: Igneous, Metamorphic

Rankings

Popularity (1–4): 3
Prevalence (1–3): 2
Demand (1–3): 2

Crystal Forms & Aggregates

Axinite forms in characteristic, flattened tabular crystals with sharp edges, and in dense groups of such crystals. Also grainy, bladed, columnar, in platy aggregates, in rosettes of sharp crystals, and massive. Crystals are often striated or have parallel line growths.

Other ID Marks

Axinite-(Mn) from Franklin, New Jersey has a red fluorescence.

Striking Features

Color and crystal habits

Environment

In hornfels and other contact metamorphic rocks near granite intrusions, and in granite pegmatites, alpine clefts, and altered diabase.

Uses

Axinite is primarily a collectors mineral, and the sharp, transparent forms are highly collectible and valued.

Noteworthy Localities

Some of the finest Axinite crytals have come Le Bourg de Oisans, France, as large, well-formed, transparent crystals. Sharp, platy aggregates, often coated with Chlorite have come from the Medel Valley, Grischun, Switzerland. A classic locality for Axinite is the St. Just District, Cornwall, England, especially at Stamps and Jowl Zawn at Botallack. Russia has produced exceptionally well-formed, large transparent crystals, often doubly terminated from Puiva, in Saranpaul. Also in Russia is the famed locality of Dal'negorsk, Primorskiy Kray, which has produced distinct, pointy aggregates of Axinite.

In Japan, dark Axinite crystals came from the Obira mine, Ono-gun, Oita prefecture; and the Toroku mine, Takachiho, Miyazaki Prefecture. The Shigar and Tormiq Valleys, Skardu District, Baltistan, Pakistan, have produced gemmy, alpine-type formations of this mineral. Nice brown crystals for Axinite have been found in Tasmania, Australia, at Colebrook Hill.

In the U.S., the premier Axinite locality is the New Melones Dam Spillway, near Copperopolis, Calaveras Co., California, where sharp brown crystals were found in a one-time construction find. In Canada, gemmy crystals come from the Grey Cloud Claim, Hart River, Yukon Territory, Canada.

The above localities are for Axinite-(Fe), which is the common form of this mineral. The localities for the less-common Axinite types are listed below:

Axinite-(Mn) is well known at Franklin, Sussex Co., New Jersey, where it forms in honey-yellow to orange crystals that are strongly fluorescent. Other Axinite-(Mn) localities include Stig, Oslo, Norway; Dal'negorsk, Primorskiy Kray, Russia; Pachapaqui, Ancash Department, Peru; and the Iron Cap Mine, Aravaipa, Graham Co., Arizona.

Axinite-(Mg) has recently been found in phenomenal gemmy crystals, often purple but sometimes orange or bi-colored, at the Merelani Hills, Arusha, Tanzania. Axinite-(Mg) has also come from Luning, Mineral Co., Nevada.

Tinzenite forms surprisingly aesthetic specimens despite it being a rare mineral. Sharp rosettes come from the Molinello Mine, Graveglia Valley, Liguria, Italy; and a exceptionally colored examples were found in a very limited occurrence at the the Wessels Mine, Hotazel, Kalahari Manganese Fields, South Africa.