Can you help me figure out birthstones?

August is peridot.
May is emerald.
Not sure on the other two.

This is what my Webster’s Crossword Puzzle Dictionary says:
Oct. opal, tourmaline.
Aug. peridot, sardonyx.
Nov. topaz.
May emerald.

Regular opal is light in color and a form of silica. Tourmaline, also a silica, is generally black.
Peridot and sardonyx are different colors of chalcedony, forms of quartz.

Thanks.

I’m an October and I choose my birthstone to be an opal. The Gemological Institute of America says “Tourmalines have a wide variety of exciting colors with one of the widest color ranges of any gem.” The color depends on its make-up: Magnesium-rich varieties are brown to yellow, lithium-rich tourmalines are almost any color: blue, green, red, yellow, pink, etc., iron-rich tourmalines are usually black to bluish-black to deep brown. Rarely, it is colorless. Traditionally, pink is the October color of tourmaline.

Thank you.

The reason you are getting conflicting results is that there are two different birthstone charts: a traditional chart that has been around for a few centuries, and a modern chart that was created in 1912 that only includes gemstones. The traditional stone for October is opal. The modern stone is pink tourmaline.