Datolite

Chemistry: Calcium boro-silicate
Crystal system: Monoclinic; short prismatic crystals of varied habit; polycrystalline; massive.
Color: Transparent to opaque; crystalline: colorless, green, yellow and pink; massive: white, orange, pink, brown.
Hardness: 5 – 5.5
Cleavage: None; Fracture: brittle, uneven to conchoidal.
Specific gravity: 2.9 – 3.0
Refractive index: 1.625 – 1.699; Biaxial negative; 0.044
Luster: Vitreous.
Dispersion: Low
Dichroism: -
Occurrence: Igneous rock; Australia, USA, UK.

Notes
Collector’s stone; may fluoresce blue and sometimes pink or yellow; blue in short wave; usually faceted.