The special bodily relics found amongst the bone remains after the cremation of Buddha and most Arahants. The extreme heat of the fire usually causes the larger bone segments to disintegrate and break up, leaving many small, often porous and ashen white colored fragments. After a certain period, the physical elements in each piece of the bone fragments is believed to amalgamate into dense, hard, crystal-like pebbles of various hues of translucency and opacity. The crystal like sarira is believe to able to transform itself from a single pebble into multiple pebbles or from multiple pebbles fused into a single pebbles. Even the hair, which were collected when the Arahant shaved his head each month is believe able to undergone a transformation similar to the cremated bone fragments.
After the cremation of a revered monk, it is customary in Thailand to distribute the remains to monk representing the various province of the country (so that it can be placed in public shrines), the revered monk disciples, his lay follower and general public.
The transformation of the bone fragments into sarira is believed to be the cleansing effect an Arahant has on his physical body elements (khandhas). The process of investigating the dhamma in deep samadhi for the purpose gaining awakening is contributing to the cleansing of the physical body element. After the awakening the physical body elements of an Arahant will remain unpolluted by the mental defilement (greed, hatred and delusion), at the same time an intrinsic level of samadhi that steadily works to cleanse the physical body element is maintained throughout the Arahant daily activities. The duration between the day an Arahant gain awakening and the day the Arahant passes away will have an effect on whether his remain will transform into sarira, as the cleansing of his physical body elements is a slow process.