Banded Agate Jewelry Banded Agate Gemstone is a beautiful variety of agate family that comes with a band like layers of microscopic crystals. It is generally formed from the deposition of layers of silica and boasts loudly of the unique beauty of the gem. Just like any other agate variety, its formation also occurred during volcanic eruptions. Over time, layers of different inclusions created recognizable bands on its surface. The gem today is famed for its exquisite appearance and cherished in jewelry pieces.