Tinzenite - Ca₂Mn²⁺₄Al₄[B₂Si₈O₃₀](OH)₂

Named for its type locality near Tinzen in Switzerland. Tinzenite is a borosilicate and belong to the axinite group. Axinite is a series name for a group of isostructural minerals, all with the same structure but different chemistry. They are named for their respective enrichment in either iron, magnesium and manganese, except for the iron manganese intermediate tinzenite. The axinite group includes:

Axinite-(Fe) or ferroaxinite, Ca₂Fe^²⁺Al₂BOSi₄O₁₅(OH)
Axinite-(Mg) or magnesioaxinite, Ca₂MgAl₂BOSi₄O₁₅(OH)
Axinite-(Mn) or manganaxinite, Ca₂Mn²⁺Al₂BOSi₄O₁₅(OH)
Tinzenite, Ca₂Mn²⁺₄Al₄[B₂Si₈O₃₀](OH)₂.

Tinzenite is found in just a handful of localities as a constituent in manganese-bearing ophiolites that have been metamorphosed as well as in quartz veins running through chert in greenschist facies.

Optical properties:

• Form: Flattened wedge shaped crystals, often with a spatula or knife-like shaped edge. Also as granular and as parallel bladed aggregates.
• Color: Is commonly a lilac brown but also yellow, yellow-orange, gray, pale blue and even black.
• Relief: High.
• Interference colors: Low (pale gray-brown).

tinzenite2020(2).jpg

Aggregate of yellowish orange prismatic t inzenite crystals associated with quartz. Tinzen, Sursass Valley, Switzerland. From RRUFF.

Aggregate of yellowish orange prismatic t inzenite crystals associated with quartz. Tinzen, Sursass Valley, Switzerland. From RRUFF.

Bibliography

• Bucher, K., & Grapes, R. (2011). Petrogenesis of metamorphic rocks. Springer Science & Business Media.
• Fossen, H. (2016). Structural geology. Cambridge University Press.
• Howie, R. A., Zussman, J., & Deer, W. (1992). An introduction to the rock-forming minerals (p. 696). Longman.
• Passchier, Cees W., Trouw, Rudolph A. J: Microtectonics (2005).
• Philpotts, A., & Ague, J. (2009). Principles of igneous and metamorphic petrology. Cambridge University Press.
• Shelley, D. (1993). Igneous and metamorphic rocks under the microscope: classification, textures, microstructures and mineral preferred-orientations.
• Vernon, R. H. & Clarke, G. L. (2008): Principles of Metamorphic Petrology. Cambridge University Press.
• Vernon, R. H. (2018). A practical guide to rock microstructure. Cambridge university press.

Photo
Brown tinzenite crystals. Apuan Alps, Tuscany, Italy. PPL image, 2x (Field of view = 7mm)	Brown tinzenite crystals. Apuan Alps, Tuscany, Italy. PPL image, 2x (Field of view = 7mm)	Brown-gray tinzenite crystals. Apuan Alps, Tuscany, Italy. XPL image, 2x (Field of view = 7mm)
Brown tinzenite crystals. Apuan Alps, Tuscany, Italy. PPL image, 2x (Field of view = 7mm)	Brown-gray tinzenite crystals. Apuan Alps, Tuscany, Italy. XPL image, 2x (Field of view = 7mm)	Brown tinzenite crystals. Apuan Alps, Tuscany, Italy. PPL image, 2x (Field of view = 7mm)
Brown-gray tinzenite crystals. Apuan Alps, Tuscany, Italy. XPL image, 2x (Field of view = 7mm)	Brown tinzenite crystals. Apuan Alps, Tuscany, Italy. PPL image, 2x (Field of view = 7mm)	Brown-gray tinzenite crystals. Apuan Alps, Tuscany, Italy. XPL image, 2x (Field of view = 7mm)
. Brown-gray tinzenite crystals. Apuan Alps, Tuscany, Italy. PPL image, 2x (Field of view = 7mm)	Brown-gray tinzenite crystals. Apuan Alps, Tuscany, Italy. PPL image, 2x (Field of view = 7mm)	Brown-gray tinzenite crystals. Apuan Alps, Tuscany, Italy. PPL image, 2x (Field of view = 7mm)
Brown-gray tinzenite crystals. Apuan Alps, Tuscany, Italy. PPL image, 2x (Field of view = 7mm)	Brown-gray tinzenite crystals. Apuan Alps, Tuscany, Italy. XPL image, 2x (Field of view = 7mm)	Brown-gray tinzenite crystals. Apuan Alps, Tuscany, Italy. XPL image, 2x (Field of view = 7mm)
Brown-gray tinzenite crystals. Apuan Alps, Tuscany, Italy. XPL image, 2x (Field of view = 7mm)	Brown-gray tinzenite crystals. Apuan Alps, Tuscany, Italy. PPL image, 2x (Field of view = 7mm)	Brown-gray tinzenite crystals. Apuan Alps, Tuscany, Italy. XPL image, 2x (Field of view = 7mm)
Brown-gray tinzenite crystals. Apuan Alps, Tuscany, Italy. PPL image, 2x (Field of view = 7mm)	Brown-gray tinzenite crystals. Apuan Alps, Tuscany, Italy. XPL image, 2x (Field of view = 7mm)	Brown-gray tinzenite crystals. Apuan Alps, Tuscany, Italy. PPL image, 2x (Field of view = 7mm)

Metamorphic Minerals

Texture and Microstructure

Metamorphic Rocks

Tinzenite - Ca2Mn2+4Al4[B2Si8O30](OH)2

Tinzenite - Ca₂Mn²⁺₄Al₄[B₂Si₈O₃₀](OH)₂