More legislation on how to affix an altar in the sanctuary, and what materials should be used for its construction:
§ 57 § The altar is the natural focal point of the sanctuary and is to be “freestanding to allow the [priest] to walk around it easily and Mass to be celebrated facing the people.”(GIRM 299)Ordinarily, it should be fixed (with the base affixed to the floor) and with a table or mensa made of natural stone,(RDCA IV, 9; Cf. GIRM 301, canon law 1235, 1236a) since it represents Christ Jesus, the Living Stone (1 Pt 2:4). The pedestal or support for the table may be fashioned from “any sort of material, as long as it is becoming and solid.”(GIRM 301; cf. canon law 1236) In the United States it is permissible to use materials other than natural stone for a fixed altar, provided these materials are worthy, solid, properly constructed, and subject to the further judgment of the local ordinary.(GIRM 301) Parishes building new churches must follow the directives of the diocesan bishop regarding the kind of altar chosen and suitable materials for new altars.
A few very brief comments:
Note that the mensa should be stone, but that a composite composition is possible, if made of all “worthy” materials.
Within the elements of universal legislation, the diocesan bishop may give additional directives, which should be followed.
And a personal remembrance. I found the altar at Our Lady of the Genesee Abbey to be striking when I first visited there as a college student. The guestmaster described that it was brought in from overhead by crane before the roof was complete.
All texts from Built of Living Stones are copyright © 2000, United States Conference of Catholic Bishops, Inc. All rights reserved. Used with permission.