12 mm Fire Agate, 10mm White Lava (Tuff), and 5mm Baroque Fresh Water Pearls; this is a hand-knotted 25 inch necklace.
Volcanic ash is caused by explosive eruption of magma in the throat of a volcano, as the magma decompresses near the surface. Tuff is volcanic ash that has fallen and welded together into a solid mass of stone. The welding occurs when the temperature of the ash is above 1,100°F. Depending on the chemical composition of the magma, the resultant stone can be various shades of tan, black, or white. Depending on the temperature and pressure during the welding process and the fineness of the ash, the stone can have large voids and spaces (commercial “lava rock”), or very small voids (Tuff). If the voids are large enough, the result is call ‘pumice’ and is often light enough to float on water.
Depending on the depth and temperature of the magma, there are different types of tuff, ranging from pumice (almost unconsolidated) to diamond containing kimberlite. The chemical and mineralogical composition varies all over the map, as well.
Tuff has been used since ancient times as a construction material by people as disparate as the Romans and the Easter Islanders.