72 Jewels And Gems

Welcome To 72 Jewels And Gems

Chemical Formula	(Fe,Mn)(Ta,Nb)_2O_6
Color	Dark black to brown
Crystal System	Orthorhombic
Hardness	6.0 to 6.5 on the Mohs scale
Density	6.0 to 8.2 g/cm^3
Cleavage	Imperfect, basal
Fracture	Conchoidal to subconchoidal
Streak	Brownish-red to black
Luster	Submetallic to resinous
Transparency	Opaque
Refractive Index	nα = 2.150, nβ = 2.240, nγ = 2.270
Birefringence	δ = 0.120
Pleochroism	Weak to moderate
Specific Gravity	6.2 to 7.8
Magnetic	Weakly magnetic
Radioactivity	Non-radioactive
Habit	Prismatic, granular, massive