Humites - nMg₂SiO₄*Mg(F, OH)₂

The term "humites" as used by mineralogists refers to four minerals that have the general formula nMg₂SiO₄*Mg(F, OH)₂, where n= 1, 2, 3, or 4. The individual mineral names are:

• Norbergite, n = 1, named from the Norberg locality, Vasmanland, Sweden;
• Chondrodite, n = 2, named from the Greek word meaning "a grain" alluding to the granular texture of the material as it occurs in aggregate form;
• Humite, n = 3, named after Sir Abraham Hume;
• Clinohumite, n = 4.

The humite group consist of minerals with similar structure, chemistry and physical properties. Unlike many other groups, there is limited chemical exchange between the individual species in the group; instead the group consists of four polysomatic series (a series of minerals composed of the same structurally or chemically distinct layers in different ratios or different sequences). The humite group is structurally related to the olivine group, and the humite structure can be expressed as an olivine structure with ordered M(OH,F)₂ layers (norbergite layers) between the olivine layers.

The Humite minerals are largely confined to metamorphic contact zones between carbonate rocks (limestone, dolomite and marble) and acidic or alkaline intrusions where fluorine has been introduced by metasomatic processes.

Optical properties:

• Form: Anhedral masses are common
• Color: Colourless to pale yallow or brown
• Relief: High
• Interference colors: Moderate

humite2020(1).jpg

Red humites crystals, Tilly Foster mine, Brewster, Putnam County, New York, USA. From RRUFF.

Red humites crystals, Tilly Foster mine, Brewster, Putnam County, New York, USA. 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
Yellow chondrodite crystals, green hercyinite and calcite in a metamorphosed limestone xenolith from Vesuvius (Italy). PPL image, 2x (Field of view = 7mm)	Chondrodite crystals (high interference colors) and calcite in a metamorphosed limestone xenolith from Vesuvius (Italy). XPL image, 2x (Field of view = 7mm)	Chondrodite crystals (high interference colors) and calcite in a metamorphosed limestone xenolith from Vesuvius (Italy). XPL image, 2x (Field of view = 7mm)
Yellow chondrodite crystals, green hercyinite and calcite in a metamorphosed limestone xenolith from Vesuvius (Italy). PPL image, 2x (Field of view = 7mm)	Chondrodite crystals (high interference colors) and calcite in a metamorphosed limestone xenolith from Vesuvius (Italy). XPL image, 2x (Field of view = 7mm)	Yellow chondrodite crystals, green hercyinite and calcite in a metamorphosed limestone xenolith from Vesuvius (Italy). PPL image, 2x (Field of view = 7mm)
Chondrodite crystals (high interference colors), isotropic hercynite and calcite in a metamorphosed limestone xenolith from Vesuvius (Italy). XPL image, 2x (Field of view = 7mm)	Yellow chondrodite crystals, green hercyinite and calcite in a metamorphosed limestone xenolith from Vesuvius (Italy). PPL image, 10x (Field of view = 2mm)	Chondrodite crystals (high interference colors), isotropic hercynite and calcite in a metamorphosed limestone xenolith from Vesuvius (Italy). XPL image, 10x (Field of view = 2mm)
Yellow chondrodite crystals, green hercyinite and calcite in a metamorphosed limestone xenolith from Vesuvius (Italy). PPL image, 10x (Field of view = 2mm)	Chondrodite crystals (high interference colors), isotropic hercynite and calcite in a metamorphosed limestone xenolith from Vesuvius (Italy). XPL image, 10x (Field of view = 2mm)	Yellow chondrodite crystals, green hercyinite and calcite in a metamorphosed limestone xenolith from Vesuvius (Italy). PPL image, 10x (Field of view = 2mm)
Yellow chondrodite crystals, green hercyinite and calcite in a metamorphosed limestone xenolith from Vesuvius (Italy). PPL image, 10x (Field of view = 2mm)	Chondrodite crystals (high interference colors), isotropic hercynite and calcite in a metamorphosed limestone xenolith from Vesuvius (Italy). XPL image, 10x (Field of view = 2mm)	Yellow chondrodite crystals, green hercyinite and calcite in a metamorphosed limestone xenolith from Vesuvius (Italy). PPL image, 10x (Field of view = 2mm)
Chondrodite crystals (high interference colors), isotropic hercynite and calcite in a metamorphosed limestone xenolith from Vesuvius (Italy). XPL image, 2x (Field of view = 7mm)	Colorless Chondrodite crystals and calcite in a metamorphosed limestone xenolith from Vesuvius (Italy). PPL image, 2x (Field of view = 7mm)	Chondrodite crystals (high interference colors) and calcite in a metamorphosed limestone xenolith from Vesuvius (Italy). XPL image, 2x (Field of view = 7mm)
< Yellow chondrodite crystals, green hercyinite and calcite in a metamorphosed limestone xenolith from Vesuvius (Italy). PPL image, 2x (Field of view = 7mm)	Chondrodite crystals (high interference colors), isotropic hercynite and calcite in a metamorphosed limestone xenolith from Vesuvius (Italy). XPL image, 2x (Field of view = 7mm)	Small humite crystals (high interference colors) in a marble. XPL image, 10x (Field of view = 2mm)
Small humite crystals (high interference colors) in a marble. XPL image, 10x (Field of view = 2mm)	Small humite crystals (high interference colors) in a marble. XPL image, 10x (Field of view = 2mm)	Small humite crystals (high interference colors) in a marble. XPL image, 10x (Field of view = 2mm)
Small humite crystals (high interference colors) in a marble. XPL image, 10x (Field of view = 2mm)	Small humite crystals (high interference colors) in a marble. XPL image, 10x (Field of view = 2mm)	Small humite crystals (high interference colors) in a marble. XPL image, 10x (Field of view = 2mm)
Small humite crystals (high interference colors) in a marble. XPL image, 10x (Field of view = 2mm)	Small humite crystals (high interference colors) in a marble. XPL image, 10x (Field of view = 2mm)	Small humite crystals (high interference colors) in a marble. XPL image, 10x (Field of view = 2mm)

Metamorphic Minerals

Texture and Microstructure

Metamorphic Rocks

Humites - nMg2SiO4*Mg(F, OH)2

Humites - nMg₂SiO₄*Mg(F, OH)₂