How to Identify a Thunderegg

Know the size of a thunderegg. Thundereggs can vary in size, ranging from 2.5 cm in diameter to over 91 cm in diameter. They can weigh less than 28 g to over a ton. Most thundereggs, however, are between 5 and 15 cm in diameter or the size of a baseball.

Observe the outer shell of a thunderegg. The outer shell of a thunderegg is often dull and brownish or red in color. It is usually knobby and may have a ribbed pattern.

Slice open a thunderegg and look at the inside of the outer shell of a thunderegg. The inside of the outer shell may be lined with "transitional" materials. This lining is usually made of iron or manganese and it may also have a thin coating of chalcedony or opal.

Marvel at the center of the thunderegg. The centers of thundereggs are beautiful and highly sought after by collectors. They are usually made of chalcedony or opal and may have many colors and patterns. They may also have inclusions or crystals of other minerals such as quartz and calcite.

Understand where thundereggs may be found. You'll only find them in areas of previous volcanic activity. Therefore, you should not look for thundereggs unless you are in an area where other volcanic rocks are found.