Keilim 6:2-3

Keilim 6:2

A stone on which one would place a pot - i.e., on the stone and on an oven, or on the stone and on a mini-stove, or on the stone and on a stove - is susceptible to ritual impurity. If he places the pot on the stone and on another, unattached stone, on the stone and on a protruding rock, or on the stone and on a wall, it is insusceptible. Such was the stove used by the nazirim (nazirites) in Jerusalem, which faced a rock. As far as butchers’ stoves, in which stones are placed side by side, if one of the stones was rendered ritually impure, the others are unaffected.

Keilim 6:3

Let’s say that three stones were made into two stoves. If one of the outer stones was rendered impure, then the part of the middle stone that serves the unclean stone is unclean but the part that serves the clean stone remains clean. If the ritually-clean stone is removed, then the middle stone is considered completely subordinate to the unclean stone. If the unclean stone is removed, then middle stone is considered completely subordinate to the clean stone. If the two outer stones are both rendered impure, then if the middle stone is large, each outer stone is granted a portion of it sufficient to support a pot and the rest is clean. If the middle stone is small, then all of it is ritually unclean. If the middle stone is removed, then if a large vat could be placed on the two remaining stones, they are unclean; if the middle stone is returned to its place, they are all purified. If the middle stone was coated with clay, it is rendered susceptible to ritual impurity when it is heated to a temperature that is sufficient to cook an egg on it.