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Apache tear obsidian
Obsidian is rapidly-cooled lava, and these Apache Tears are little rounded lumps that are found in a soft perlite near Superior, Arizona. Perlite forms when a lava is heavily soaked in water, and the obsidian nodules are the unaffected cores of each perlite fracture nodule.
The name comes from a story where Apache warriors rode off a cliff rather than be captured by the US cavalry, and the tears of their wives and children turned to stone where they fell. May not be 100% true.
Obsidian lumps are around 3cm across.