Polishing Up Your Mineral Vocabulary

Will Estavillo, minerals curator at the Natural History Museum in Balboa Park and author of his own guide to California minerals, offers these descriptions of rocks to help you tell wonderstone from bloodstone and quartz from quartzite:

Agate: Agates can be mixed with jasper or exist by themselves. They are typically carnelian in color with light pink and red tones. Sometimes they are white.

Andesite: This is a green rock named for the Andes Mountains.

Bloodstone: This is a jasper that combines both red and green in the same stone. Typically, the basic stone is green with red flecks.

Breccia: This volcanic rock is really a combination of other rocks blown apart in volcanic explosions. The rocks will be a terrazzo of angular fragments within the pebble.

Brick and bottles: Yes, brick and bottles. Bottle pieces are often tumbled in the waves. The result is clear or green pebbles or shards. Bricks sometimes become round red cobble after time in the waves.

Garnet, zircon, gold: These materials will be found among the black sand of the beach. Most specimens will be very small. Garnet will be red, zircon clear, and gold, well, gold.

Jasper: This is a red variety of very fine grained quartz material, or a green variety of quartz.

Moonstone: This is one of June’s birthstones. Moonstone is white like quartz, but, when turned in sunlight, an iridescence will shine from within.

Petrified wood: This is somewhat rare. Petrified wood on the beach will have been rolled into cobble and will have a woody grain.

Quartz: This is common on area beaches. Quartz is one of two white stones you are likely to find. The other will be moonstone.

Quartzite: These ancient rocks are similar to quartz, but have a sugary feel and appearence.

Rhyolite: Some rhyolites are called wonderstones because of their colorful combinations of light and dark bands. These can be pink, tan or brown.