BABINGTONITE

Babingtonite – Ca2(Fe,Mn)FeSi5O14(OH) – is a fairly rare inosilicate. It is not important as an ore, but as a collector’s mineral it fetches quite high prices, hundreds of dollars per piece.

It may contain Al, Mg, Na, and Ti. Forms epitaxies with hedenbergite and a series with manganobabingtonite. It exhibits weak magnetism.

1. Characteristics

Crystal system: Triclinic pinacoidal.          

Color: Dark greenish-black.     

Habit: Short, tabular prismatic crystal, may form subparallel or radial aggregates. Crystals up to 3 cm.

Cleavage: {001} perfect, {001} good, {100} good. Striations!

Tenacity: Brittle.        

Twinning: No.       

Fracture: Irregular.       

Mohs Hardness: 5.5 – 6

Parting: No.         

Streak: No information available.         

Lustre: Vitreous.          

Diaphaneity: Transparent.           

Density (g/cm³): 3.3

           

2. Geology and Deposits

Babingtonite occurs in cavities (vesicles) of mafic volcanic rocks (basalts, diabases, etc.). Also in cavities related to gneiss.

It is found also in veins that cut through granitic pegmatites and diorites.  Can be found in skarns.

 

3. Mineral Associations

It is associated with minerals typical of mafic rock cavities, such as quartz, prehnite, calcite, apophyllite and zeolites (heulandite-Ca, stilbite-Ca).

Also with epidote, albite, orthoclase, garnet, “hornblende” and byssolite.

 

4. Transmitted Light Microscopy

Refraction indices:  nα:  1,700     nβ: 1,710       nγ: 1,725

PLANE POLARIZED LIGHT – PPL

Color / Pleochroism: Pleochroic:

x = deep green
y = lilac brown
z = pale to deep brown.

Relief: High.           

Cleavage: {001} perfect.          

Habits: Short prismatic structure, can form radial aggregates.

CROSSED POLARIZED LIGHT – XPL

Birefringence and Interference Colors: Maximum birefringence of 0.025, corresponding to interference colors up to the beginning of the 2nd order: yellowish, yellow, orange, red, blue and blue-green. 

Extinction: No information available, propably oblique.           

Elongation sign: No information available, probably not diagnostic.

Twins: No.         

Zoning: No.             

CONVERGENT LIGHT

Character: B(-)          

2V angle: 50º         

Alterations: No information available.          

May be confused with: Few other minerals, due to the very typical pleochroism and paragenesis.         

Caption.

5. Reflected Light Microscopy

Reflected Light Microscopy is obviously not the recommended analytical method for identifying babingtonite. However, it is important to create a polished slide or section to identify the opaque minerals that occur associated with babingtonite, such as magnetite.

Sample preparation:        

PLANE POLARIZED LIGHT – PPL

Reflection color:        

Pleochroism:       

Reflectivity:         

Bireflectance:        

CROSSED POLARIZED LIGHT – XPL

Isotropy / Anisotropy:         

Internal reflections:       

May be confused with:        

General Characteristics: 

Caption.