A lingam may be made of clay (mrinmaya), metal (lohaja), precious stone (ratnaja), wood (daruja), stone (sailaja, most common), or a disposal material (kshanika). The construction method, proportions and design is described in Shaiva Agama texts. The lingam is typically set in the center of a pindika (also called yoni or pithas, symbolizing Shakti). A pindika may be circular, square, octagonal, hexagonal, duodecagonal, sixteen sided, alliptical, triangular or another shape. Some lingams are miniaturized and they are carried on one's person, such as by Lingayats in a necklace. These are called chala-lingams. The Hindu temple design manuals recommend geometric ratios for the linga, the sanctum and the various architectural features of the temple according to certain mathematical rules it considers perfect and sacred. Anthropologist Christopher John Fuller states that although most sculpted images (murtis) are anthropomorphic or theriomorphic, the aniconic Shiva Linga is an important exception.