This listing is for a similar block of Periwinkle Fiber Optic Glass 

It measures around 4 7/8 inches x 4 5/8 inches x 1 1/4 inches

It weighs around 2.6 pounds.

Fiber optic glass is man-made glass composed of millions of glass fibers that have been fused together into a block. This creates a reflective characteristic known as cat-eye. This material can be slabbed easily with a diamond blade. It is a great material for making cabochons as well as flint knapping into arrowheads, spears, or other shapes.

Photos were taken under sunlight while wet

We have been selling rough rock and slabs in Quartzsite, Arizona for over 20 years.