This Volcanic Agate skull weighs 3.4 lb and has a hardness of about 6-7 since it is an agate. When lava cooled water seeped into holes that were created by bubbles and deposited iron, quartz, and other minerals. Agates is classified by its striking formation of Chalcedony layered with crystalline quartz creating bands of color and translucency. The greenish reaction from UV 365nm wavelength is due to uranyl ion that gets excited by the uv wave. 
Please visit alchemistofstones.com for more products.