Addendum:
According to the General Instruction of the Roman Missal, it seems that “”the celebration of the Eucharist in a sacred place is to be carried out on an altar; but outside a sacred place, it may be carried out on a suitable table, always with the use of a cloth, a corporal, a cross, and candles.”
The Altar and Its Appointments
The altar on which the Sacrifice of the Cross is made present under sacramental signs is also the table of the Lord to which the People of God is called together to participate in the Mass, as well as the center of the thanksgiving that is accomplished through the Eucharist.
The celebration of the Eucharist in a sacred place is to be carried out on an altar; but outside a sacred place, it may be carried out on a suitable table, always with the use of a cloth, a corporal, a cross, and candles.
It is appropriate to have a fixed altar in every church, since it more clearly and permanently signifies Christ Jesus, the living stone (1 Pt 2:4; cf. Eph 2:20). In other places set aside for sacred celebrations, the altar may be movable.
An altar is called “fixed” if it is attached to the floor so as not to be removeable; otherwise it is called “moveable.”
The altar should be built apart from the wall, in such a way that it is possible to walk around it easily and that Mass can be celebrated at it facing the people, which is desirable wherever possible. The altar should, moreover, be so placed as to be truly the center toward which the attention of the whole congregation of the faithful naturally turns.[116] The altar is usually fixed and is dedicated.
An altar whether fixed or movable is dedicated according to the rite prescribed in the Roman Pontifical; but it is permissible for a movable altar simply to be blessed.
In keeping with the Church’s traditional practice and the altar’s symbolism, the table of a fixed altar is to be of stone and indeed of natural stone. In the dioceses of the United States of America, however, wood which is worthy, solid, and well-crafted may be used, provided that the altar is structurally immobile. The supports or base for upholding the table, however, may be made of any sort of material, provided it is worthy and solid.
A movable altar may be constructed of any noble and solid materials suited to liturgical use, according to the traditions and usages of the different regions.
The practice of placing relics of Saints, even those not Martyrs, under the altar to be dedicated is fittingly retained. Care should be taken, however, to ensure the authenticity of such relics.
In building new churches, it is preferable to erect a single altar which in the gathering of the faithful will signify the one Christ and the one Eucharist of the Church.