An altar is a stone block or pillar topped with a flame. The flame, though part of the definition of the charge, is nonetheless sometimes specified: e.g., “an altar flammant”. The heraldic altar appears to represent a Pagan altar, rather than the Christian or Jewish altars [Franklyn 7]; it’s found in the arms of Tendryngg, 1340 [DBA3 357]. See also edifice.
Arthur Glendower bears: Or, between two lions combatant azure an altar sable flammant gules.
Una MacRobert bears: Vert, an altar argent between three vols Or.
Asa Gormsdottir bears: Per chevron sable and gules, four bezants and an altar argent enflamed Or.