Serendibite

Serendibite is an extremely rare silicate mineral that was first discovered in 1902 in Sri Lanka by Dunil Palitha Gunasekera and named after Serendib, the old Arabic name for Sri Lanka.

Serendibite
A relatively sharp, vitreous black crystal of serendibite from Le Oo, in Mogok Township, measures: 16 x 13 x 8 mm
General
Category	Inosilicates
Formula (repeating unit)	(Ca,Na)2(Mg,Fe2+)3(Al,Fe3+)3[O2|(Si,Al,B)6O18]
Strunz classification	9.DH.40
Dana classification	69.2.1a.6
Crystal system	Triclinic
Crystal class	Pinacoidal (1) (same H-M symbol)
Space group	P1
Identification
Color	pale yellow, blue-green, greyish blue, black
Twinning	Polysynthetic on {0-11} is common
Cleavage	None Observed
Mohs scale hardness	6.5 - 7
Luster	Vitreous
Streak	White
Diaphaneity	Transparent, Translucent,Opaque
Specific gravity	3.42 - 3.52 (measured) 3.47 (calculated)
Optical properties	Biaxial (+)
Refractive index	1.701 - 1.706
Pleochroism	Visible,strong, color: green, blue, yellow, bluegreen, light yellow
2V angle	Measured: 80°
Dispersion	strong
References	[1][2]

The mineral is found in skarns associated with boron metasomatism of carbonate rocks where intruded by granite. Minerals occurring with serendibite include diopside, spinel, phlogopite, scapolite, calcite, tremolite, apatite, grandidierite, sinhalite, hyalophane, uvite, pargasite, clinozoisite, forsterite, warwickite and graphite.[2]

Crystal from Mogok, Myanmar, size: 1 cm x 0.7 cm x 0.7 cm