April 28, 2012

Geology Word of the Week: U is for Ulexite

Posted by Evelyn Mervine

My sample of ulexite aka "TV Rock."

def. Ulexite:
1. Hydrated sodium calcium borate hydroxide (formula: NaCaB5O6(OH)6•5(H2O) ), a silky, brittle, generally white evaporate mineral  which often crystallizes in the form of densely-packed fibers that transmit light along the long axis of the mineral.

2. A party trick rock. Have any party guests who think that geology isn’t awesome? Just pull out your fibrous ulexite sample and say, “Hey look, I have a fiber optic rock.” Then watch the fun– the geology fun– begin.


Ulexite really does have remarkable optical properties, as the photos below demonstrate. Personally, I think that the fiber optic images produced by ulexite are even more fun and interesting than the double images caused by refraction in calcite.

Another picture of my ulexite sample, with keys for scale.

The word "Hyundai "through ulexite.

Dinosaur origami box, viewed through ulexite.

A side (short axis) view of ulexite, showing the fibers but no optical transmission.

I bought my ulexite sample at a rock sale. Does anyone know of good places to collect ulexite in the field?