What is this rock made of?

Jerry Coyne’s Why Evolution is True webiste uncovers a lot of gems on the internet. Recently, he posted a link to Nasa’s billion-pixel panoramic photo (composite) from the Curiosity rover. You can  take a close look at a great deal of Martian landscape using their viewer. Just below the panorama are links that will drag you to come intriguing places in the image (a shiny white object in the sand, what seriously looks like a Martian bird – I can’t stand not knowing what this really is, etc.) I also found a rock that the rover had broken open that exposed a shiny, light-colored interior (above).