MUMMEROY'S LAPIDARY BORROWING [Summons a 150-200 pound stone, temporarily. ] In the plainest terms, Mummeroy's Lapidary Borrowing summons a flat-bottomed boulder weighing about as much as a human being. The boulder appears a handspan or so above the ground (then falls, of course), and in the caster's near vicinity.
It is not a surgically precise conjuration, and so it is difficult to aim it finely enough to crush an opponent's foot, e.g. But it's accurate enough to reliably use to test for pit traps, add ballast to a ship, or block a doorway. The stone remains in existence for several minutes—sometimes several hours—whereupon it vanishes as instantly as it appeared.
In the hands of an experienced caster, this summoning may be accomplished multiple times in a row, producing four, ten, or even as many as 15 boulders that coexist at roughly the same time. Interestingly, as Mummeroy himself noted, when the summoning is performed in this manner, it is clear that all the summoned stones are precisely identical. It is postulated that the stones are being borrowed from other parallel and quite similar planes of existence—hence the name. Professor DiVestiga says that, to learn the spell, a student must wander outside and find the stone they wish to summon in the future, bonding with it using the proper ritual. This stone will never change (though the spell may be learned multiple times for different stones), and that specific stone will forever be the property of that caster in every dimension. The stone-bonding ritual is found in a handful of the more complete incunabula, including The Book of Throst, currently held in the Library of Shadows.
Known Variations Ramala's Spherical Lapidary Exception is a version of the conjuration that summons forth a largely spherical stone, which is almost entirely useless for blocking a door, but is definitely useful for rolling down a potentially trapped hallway, or for sending downhill in hopes of sparking an avalanche.
Lubya of Krumholz's Marvelous Mineral Raft is a variation that summons a wall of pumice (ten feet by ten feet and one foot thick) that weighs the same as other versions of the spell, but provides more cover—and it floats in water, so it makes a serviceable emergency float. It is, however, quite frangible.
Eller's Efficacious Millstone summons a millstone, and this can be summoned either on end (when you want it to be able to roll) or on its side (when you just need weight). It is therefore possibly the most useful and flexible of the stone summonings, and is widely in demand.
Perhaps the most interesting variant is Thyra of Ivor's Immediate Thronery, which summons, not a boulder, but a VERY heavy plush high-backed chair from the throneroom of Halagast VI. (Thyra, Halagast's court wizardess, never liked to be without comfortable seating, even when in the wilderness.) For all its luxury, the chair is quite sturdy, and a dozen of them sufficed to bar an important door during the Zombie Siege of Nunheim.
Common Mishaps The most common error that occurs in a miscast of this spell is that the stone appears in the caster's own space, which is quite awkward, and disruptive, and has resulted in many a crushed foot. Another stranger mishap is that the stone appears and immediately vanishes without touching down...and then a displacement warp appear beside the caster, trapping them and attempting to bring them into the stone's dimension. It is a smallish stone-sized warp that is easily resisted by most fullsized casters, but it can take several distracted moments to close, removing the caster from other activity during that time.
[Difficulty 10. Lasts 10 minutes per level. May be recast once per caster level in every subsequent round until a casting fails, without using up a spell slot.]