National Geographic : 1966 Jan
Crushing force, perhaps millions of years ago, shattered portions of trem olite-actinolite. The small granules, rotated during crushing, have align ments different from the solid center; thus light from them is affected differ ently, many appearing brown instead of yellow, red, and blue. Snakes writhe in a lava bath. Formed in molten rock, olivine fractures when it cools and hardens. Water seeps into the cracks and sets off chemical re actions that alter the reddish-appearing olivine to ser pentine (green). The author inserted a quartz wedge into the microscope to enhance the colors of this rock, which otherwise appears dull.