Howlite

Chemistry: Silico-borate of calcium.
Crystal system: Monoclinic; massive; compact nodules.
Color: Semi translucent to opaque; white material veined with dark gray or black.
Hardness: 3.5
Cleavage: -
Specific gravity: 2.52 (2.52 – 2.57)
Refractive index: 1.53 mean; aggregate.
Luster: Vitreous to sub-vitreous.
Dispersion: -
Dichroism: -
Occurrence: USA

Notes
Ornamental material; frequently dyed blue (turquoise, lapis); less often other colors (coral, jade); identification based on magnification, appearance (texture, color, structural markings); look for dye concentrations in cracks and grain boundaries; color, may be unstable; fluorescence: brownish yellow (short wave); some Californian material may fluoresce orange (long wave); cabochon, beads, carvings.