Buy Moss Agate from Crystals By Nature. Moss Agate embodies the lush and verdant great outdoors with its colorful green hues. A form of Chalcedony, Moss Agate is a semi-precious gemstone formed from silicon dioxide. Known as a "Grounding Stone", Moss Agate is declared to correct left-right brain imbalances and stimulate creativity. An exceptional stone for communicating with all aspects of the natural world, Moss Agate can help provide an intuitive understanding of Mother Nature's creations.