Crystal Axinite

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) 
 

Basic aluminum boro-silicate of calcium, iron, magnesium, and manganese 

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.

Colorless

6.5 - 7

Triclinic

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.
 

Transparent to nearly opaque

3.3 - 3.4

Vitreous

2,1

Conchoidal to uneven

Brittle

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

Silicates; Cyclosilicates

Color and crystal habits

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

Igneous, Metamorphic

3

2

2