Wiktionary
n. Rounded nodules of obsidian.
Wikipedia
"Apache tears" is the popular term for rounded pebbles of obsidian or "obsidianites" composed of black or dark-colored natural volcanic glass, usually of rhyolite composition and bearing conchoidal fracture. Also known by the lithologic term "marekanite", this variety of obsidian occurs as subrounded to subangular bodies up to about 2 inches in diameter, often bearing indented surfaces. Internally the pebbles sometimes contain fine bands or microlites and though in reflected light they appear black and opaque, they may be translucent in transmitted light. Apache tears fall between 5 and 5.5 in hardness on the Mohs scale.
Usage examples of "apache tears".
Quantities of quartz crystals, geodes, apache tears, jasper pebbles, moonstone beads, and….
Dean was on the other side of his father, silently playing jacks with the tiny black pebbles that are sometimes called Apache tears.