Material :

Striped translucent black obsidian

Measurements :

Comes in 7 sizes :
45 x 24 mm (1.77 x 0.94 in)
90 x 35 mm (3.54 x 1.38 in)
108 x 42 mm (4.25 x 1.65 in)
135 x 52 mm (5.31 x 2.05 in)
180 x 70 mm (7.08 x 2.76 in)
225 x 85 mm (8.86 x 3.35 in)
270 x 104 mm (10.63 x 4.09 in)