NEPTUNITE
Neptunite is a scarce, moderately complex sodium potassium lithium iron
manganese titanosilicate mineral (Na2KLi(Fe,Mn)2Ti2Si8O24).
It has a nonmetallic, slightly glassy luster, a blackish color (actually, it's
an exceedingly dark reddish black), and a reddish-brown streak. Its
crystals commonly occur as elongated, squarish rods. It has a hardness of
between 5 and 6, and it breaks along cleavage planes meeting at 80¡ and
100¡. Neptunite can be an igneous or metamorphic mineral.
Neptunite (18 mm across) on blueschist (glaucophane metamorphite), associated
with natrolite (white). Dallas Gem Mine, San Benito County, California,
USA.