agate
n//ˈæɡ.ət//agat
(countable, uncountable, mineral) A semitransparent, uncrystallized silicate mineral and semiprecious stone, presenting various tints in the same specimen, with colors delicately arranged and often curved in parallel alternating dark and light stripes or bands, or blended in clouds; various authorities call it a variety of chalcedony, a variety of quartz, or a combination of the two.
(slang, usually, in the plural) A testicle.