Chiastolite (Cross stones), bookends or specimens

Two pieces of a really unusual mineral!  The basic mineral is andalusite, and in this form when the crystals are sliced a cross of carbon is revealed.  The squarish shape is natural, with the cut faces having been polished to show off the crosses better.  I think that they can work as bookends, or as a pair of individual specimens.  The book is included.

Approximately 9/16 inch (1.4 cm) wide and tall, 5/16 inch (0.8 cm) deep.