Niocalite - (Ca,Nb)₄(Si₂O₇)(O,OH,F)₂

Niocalite, named for its composition (NIObium, CALcium), is a rare calcium niobium silicate and only three locality are known for Niocalite: Oka (the type locality), Kaiserstuhl (Germany) and Oldoinyo Lengai (Tanzania, Africa). Niocalite was first identified in 1956 by Dr. E.H.Nickel in diamond drill core from the Oka, Quebec. The rock in which the niocalite occurs is essentially a coarse, crystalline strontian calcite containing niocalite, magnetite, and apatite. The niocalite occurs as randomly oriented, coarse, prismatic crystals up to one cm in length, and occasionally even longer, embedded in the calcite. in some of the higher grade sections, niocalite constitutes about 10% of the rock.

Optical Properties:

• Habits: Prismatic with square cross sections and curved faces.
• Color: Lemon-yellow; colorless in thin section.
• Relief: High.
• Twinning: Twins are intimately intergrown.
• Birefringence: High, II order.

Yellow Niocalite crystals in a Carbonatite. Oka complex, Quebec, Canada. Image from RRUFF

Bibliography

• Cox et al. (1979): The Interpretation of Igneous Rocks, George Allen and Unwin, London.
• Howie, R. A., Zussman, J., & Deer, W. (1992). An introduction to the rock-forming minerals (p. 696). Longman.
• Le Maitre, R. W., Streckeisen, A., Zanettin, B., Le Bas, M. J., Bonin, B., Bateman, P., & Lameyre, J. (2002). Igneous rocks. A classification and glossary of terms, 2. Cambridge University Press.
• Middlemost, E. A. (1986). Magmas and magmatic rocks: an introduction to igneous petrology.
• 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.

Photo
Niocalite crystals (high relief), apatite (colorless) and calcite in a plutonic carbonatite (sovite) from Oka complex, Quebec, Canada. PPL image, 1x (Field of view = 9mm)	Niocalite crystals (high birefringence), apatite (I order gray) and calcite in a plutonic carbonatite (sovite) from Oka complex, Quebec, Canada. XPL image, 1x (Field of view = 9mm)	Niocalite crystals (high relief), apatite (colorless) and calcite in a plutonic carbonatite (sovite) from Oka complex, Quebec, Canada. PPL image, 2x (Field of view = 7mm)
Niocalite crystals (high birefringence), apatite (I order gray) and calcite in a plutonic carbonatite (sovite) from Oka complex, Quebec, Canada. XPL image, 2x (Field of view = 7mm)	Niocalite crystals (high birefringence), apatite (I order gray) and calcite in a plutonic carbonatite (sovite) from Oka complex, Quebec, Canada. XPL image, 2x (Field of view = 7mm)	Niocalite crystals (high relief), apatite (colorless) and calcite in a plutonic carbonatite (sovite) from Oka complex, Quebec, Canada. PPL image, 2x (Field of view = 7mm)
Niocalite crystals (high birefringence), apatite (I order gray) and calcite in a plutonic carbonatite (sovite) from Oka complex, Quebec, Canada. XPL image, 2x (Field of view = 7mm)	Niocalite crystals (high relief), apatite (colorless) and calcite in a plutonic carbonatite (sovite) from Oka complex, Quebec, Canada. PPL image, 2x (Field of view = 7mm)	Niocalite crystals (high birefringence), apatite (I order gray) and calcite in a plutonic carbonatite (sovite) from Oka complex, Quebec, Canada. XPL image, 2x (Field of view = 7mm)
Niocalite crystals (high relief) and calcite in a plutonic carbonatite (sovite) from Oka complex, Quebec, Canada. PPL image, 10x (Field of view = 2mm)	Niocalite crystals (high birefringence) and calcite in a plutonic carbonatite (sovite) from Oka complex, Quebec, Canada. XPL image, 10x (Field of view = 2mm)	Niocalite crystals (high relief) and calcite in a plutonic carbonatite (sovite) from Oka complex, Quebec, Canada. PPL image, 10x (Field of view = 2mm)
Niocalite crystals (high birefringence) and calcite in a plutonic carbonatite (sovite) from Oka complex, Quebec, Canada. XPL image, 10x (Field of view = 2mm)	Niocalite crystals (high birefringence), apatite (I order gray) and calcite in a plutonic carbonatite (sovite) from Oka complex, Quebec, Canada. XPL image, 10x (Field of view = 2mm)	Niocalite crystals (high birefringence), apatite (I order gray) and calcite in a plutonic carbonatite (sovite) from Oka complex, Quebec, Canada. XPL image, 10x (Field of view = 2mm)
Niocalite crystals (high relief) and calcite in a plutonic carbonatite (sovite) from Oka complex, Quebec, Canada. PPL image, 10x (Field of view = 2mm)	Niocalite crystals (high birefringence), apatite (I order gray) and calcite in a plutonic carbonatite (sovite) from Oka complex, Quebec, Canada. XPL image, 10x (Field of view = 2mm)	Niocalite crystals (high birefringence), apatite (I order gray) and calcite in a plutonic carbonatite (sovite) from Oka complex, Quebec, Canada. XPL image, 10x (Field of view = 2mm)
Niocalite crystals (high relief) and calcite in a plutonic carbonatite (sovite) from Oka complex, Quebec, Canada. PPL image, 10x (Field of view = 2mm)	Niocalite crystals (high birefringence) and calcite in a plutonic carbonatite (sovite) from Oka complex, Quebec, Canada. XPL image, 10x (Field of view = 2mm)	Niocalite crystals (high birefringence) and calcite in a plutonic carbonatite (sovite) from Oka complex, Quebec, Canada. XPL image, 10x (Field of view = 2mm)
Niocalite crystals (high birefringence) and calcite in a plutonic carbonatite (sovite) from Oka complex, Quebec, Canada. XPL image, 10x (Field of view = 2mm)	Niocalite crystals (high birefringence) and calcite in a plutonic carbonatite (sovite) from Oka complex, Quebec, Canada. XPL image, 10x (Field of view = 2mm)	Niocalite crystals (high birefringence) and calcite in a plutonic carbonatite (sovite) from Oka complex, Quebec, Canada. XPL image, 10x (Field of view = 2mm)
Niocalite crystal (high relief) and calcite in a plutonic carbonatite (sovite) from Oka complex, Quebec, Canada. PPL image, 20x (Field of view = 1mm)	Niocalite crystal (high birefringence) and calcite in a plutonic carbonatite (sovite) from Oka complex, Quebec, Canada. XPL image, 20x (Field of view = 1mm)	Niocalite crystals (high relief) and calcite in a plutonic carbonatite (sovite) from Oka complex, Quebec, Canada. PPL image, 20x (Field of view = 1mm)
Niocalite crystal (high birefringence) and calcite in a plutonic carbonatite (sovite) from Oka complex, Quebec, Canada. XPL image, 20x (Field of view = 1mm)	Niocalite crystal (high birefringence) and calcite in a plutonic carbonatite (sovite) from Oka complex, Quebec, Canada. XPL image, 20x (Field of view = 1mm)	Niocalite crystal (high birefringence) and calcite in a plutonic carbonatite (sovite) from Oka complex, Quebec, Canada. XPL image, 20x (Field of view = 1mm)
Niocalite crystal (high relief) and calcite in a plutonic carbonatite (sovite) from Oka complex, Quebec, Canada. PPL image, 20x (Field of view = 1mm)	Niocalite crystal (high birefringence) and calcite in a plutonic carbonatite (sovite) from Oka complex, Quebec, Canada. XPL image, 20x (Field of view = 1mm)	Niocalite crystal (high birefringence) and calcite in a plutonic carbonatite (sovite) from Oka complex, Quebec, Canada. XPL image, 20x (Field of view = 1mm)
Niocalite crystal (high relief) and calcite in a plutonic carbonatite (sovite) from Oka complex, Quebec, Canada. PPL image, 20x (Field of view = 1mm)	Niocalite crystal (high birefringence) and calcite in a plutonic carbonatite (sovite) from Oka complex, Quebec, Canada. XPL image, 20x (Field of view = 1mm)	Niocalite crystal (high birefringence) and calcite in a plutonic carbonatite (sovite) from Oka complex, Quebec, Canada. XPL image, 20x (Field of view = 1mm)
Niocalite crystal (high birefringence) and calcite in a plutonic carbonatite (sovite) from Oka complex, Quebec, Canada. XPL image, 20x (Field of view = 1mm)	Niocalite crystal (high birefringence) and calcite in a plutonic carbonatite (sovite) from Oka complex, Quebec, Canada. XPL image, 20x (Field of view = 1mm)	Niocalite crystal (high birefringence) and calcite in a plutonic carbonatite (sovite) from Oka complex, Quebec, Canada. XPL image, 20x (Field of view = 1mm)