Polished Volcanic Agate Heart - Choose your quantity! Uniqueness Guaranteed: Every item is one-of-a-kind, making them ideal for all projects or designs. Avg Size Range: (1.5 to 2 Inches Long) Sizes Vary Volcanic agate, sometimes also called agatized volcanic rock, forms when silica-rich fluid crystallizes into agate in pockets inside volcanic rock. Typically found near the base of older volcanoes, volcanic agate can occasionally fluoresce under UV light depending on included minerals in the host rock. Handmade items vary in size, shape, and color when selected randomly (the highest quality items are chosen first). They'll be as beautiful as those in the photos.