The chains of octahedrons are held together by individual silicate tetrahedrons but it is the octahedron chains that give topaz its crystalline shape. Topaz is the hardest silicate mineral and one of the hardest minerals in nature. None of the stronger Si-O bonds cross these planes. Topaz crystals can reach incredible size of several houndred pounds. Topaz can make very attractive mineral specimens due to their high luster, nice colors and well formed and multifaceted crystals.
Color is clear, yellow, orange, red, blue and green.
Luster is adamantine to vitreous. Transparency crystals are transparent to translucent. The termination is typically capped by a dome forming a roof like top. Another dome can modify the termination producing a point at the juncture of the two domes. A basal pinacoid can flatten the prisms termination or truncate the top of the domes.