Tsilaisite

Tsilaisite, also known as Tsilaizite, is an orangish-yellow to brownish-gold, manganese-rich variety of Elbaite Tourmaline. It was originally reported from the Tsilaisina (Tsilaizina) Mine, Tsilaisina pegmatite, on the northern side of Mt. Tsilaisina, Sahatany Pegmatite Field (Mt. Ibity area), Sahatany Valley, Vakinankaratra Region (Betafo – Antsirabé Region), Antananarivo Province, Madagascar.

These special Tourmalines from this mine are particularly rich in Manganese, up to 3% of their chemistry. While this is not enough to qualify them as a separate variety of Tourmaline, they are certainly unique among Tourmaline gems. Tsilaisite gems are very attractive due to their unique color and vary rare from this location.

Chemical Formula:	Na(Mn2+AlFe2+)3Al6[(O,OH,F)4|(OH)3|(BO3)3|Si6O18]
	Sodium Manganese Aluminum Iron Boro-Silicate Hydroxide
Molecular Weight:	(Elbaite) 916.68 gm

Composition:	(Elbaite)
	Sodium	2.51 %	Na	3.38 %	Na2O
	Lithium	1.89 %	Li	4.07 %	Li2O
	Aluminum	19.13 %	Al	36.15 %	Al2O3
	Silicon	18.38 %	Si	39.33 %	SiO2
	Boron	3.54 %	B	11.39 %	B2O3
	Hydrogen	0.44 %	H	3.93 %	H2O
	Oxygen	54.11 %	O
		100.00 %		100.00 %	= TOTAL OXIDE

 

Crystallography:	Trigonal – Ditrigonal Pyramidal
Crystal Habit:	(Elbaite) Crystals prismatic to acicular, with prominent trigonal prism and pyramid, to 1.6 m, commonly hemimorphic, striated k [0001]. Also radial, fibrous, and massive.
Twinning:	(Elbaite) Rare, on {1011} or {4041}

 

Cleavage:	Poor/Indistinct on {1120} and {1011}
Fracture:	Irregular/Uneven to Conchoidal
Tenacity:	Brittle
Moh’s Hardness:	7.5
Density:	2.90- 3.10 (g/cm3)
Luminescence:	None
Radioactivity:	Not Radioactive
Other:	Piezoelectric, pyroelectric

 

Color:	Orangish-Yellow to Brownish-Gold
Transparency:	Transparent to Translucent
Luster:	Vitreous
Refractive Index:	1.615 – 1.651  Uniaxial  ( – ); under strain may show slight biaxiality
Birefringence:	0.0180 – 0.0200
Dispersion:	n/a
Pleochroism:	None