altar stone

altar-stone, altarstone

altar stone (plural altar stones)

1. A consecrated stone that forms all or part of the mensa of an altar.
   • 1993, B. Don Taylor, The Complete Training Course for Altar Guilds, page 32:

     Some churches also have an altar stone, a separate stone set into the mensa containing a relic of a saint, although this is becoming extremely rare.

   • 2010, I.S. Cooper, Ceremonies of The Young Rite, page 305:

     When the altar stone is already in place upon the altar at which it is to be used, or forms the top of the altar, and when the church or oratory is not to be consecrated at this time, the consecration of the altar stone may take place publicly preceding a celebration of the Holy Eucharist by the Bishop.

   • 2011, Saul M. Olyan, Social Inequality in the World of the Text, page 191:

     This statement indicates that according to Exod 20:25, altar stones, like most sacrifices and like priests, are sanctified.

When the entire upper surface of the altar is a single stone, this can be called either the altar stone, or simply altar.