300. An altar, whether fixed or movable, should be dedicated according to the rite prescribed in the Roman Pontifical; but it is permissible for a movable altar simply to be blessed.
Ordinarily, an altar will be of stone–not the crushed and refabricated variety. One parish I served had such an altar: marble veneer covering cinderblock.
301. In keeping with the Church’s traditional practice and with what the altar signifies, the table of a fixed altar should be of stone and indeed of natural stone. In the Dioceses of the United States of America, wood which is dignified, solid, and well-crafted may be used, provided that the altar is structurally immobile. As to the supports or base for supporting the table, these may be made of any material, provided it is dignified and solid.
In the US, wood is permissible for the mensa. My parish has such an altar–the base is also a nice complementary wood. I’ve also seen altars that incorporate both natural stone and wood.
A movable altar may be constructed of any noble and solid material suited to liturgical use, according to the traditions and usages of the different regions.
Thoughts on the make-up of altars?