Agate Quartz Geode Slice Brown 6.5 - 7.5 inches. Agate is a very fine grained form of Quartz. It grows within volcanic lava bubbles known as geodes. Diamond saws are used to slice the Agate it is then ground to remove any imperfections then polished and dyed to enhance and display the beautiful natural banding within.. The size, shape and colour of the product you will receive may differ slightly from the product shown in the image.