Guess the Cover of American Laboratory—August 2012

Correctly identify this month’s cover image and be entered to win a $10 Amazon gift card (one entry per person; you must be 18 years of age to be eligible. See contest rules at

The cover of the August issue depicts an object that is highly regarded by petrologists, rockhounds, and decorators. This image was captured on a polarized light microscope under crossed polars. In preparation the subject was thinly polished to approximately 30 μm thickness, mounted to a glass slide, and coverslipped. Original magnification was 250×.

What do you think it is? Enter by leaving your answer in the comments section below. Stay tuned for the answer and for next month’s cover image!