Stoneskin

4th-Level Transmutation
Casting Time: 1 action
Range: Touch
Components: VSM($) (diamond dust worth 100 gp)
Duration: (C) 1 hour

This spell turns the flesh of a willing creature you touch as hard as stone. Until the spell ends, the target has resistance to nonmagical bludgeoning, piercing, and slashing damage.

When you cast the spell, you can choose to consume the diamond dust used in its casting. If you do, the target gains resistance to all bludgeoning, piercing, and slashing damage until the spell ends instead.

At Higher Levels. When you cast this spell using a spell slot of 5th level or higher, you can target one additional creature for each slot level above 4th.

Source: PHB 278, SRD

Changelog

Added upcasting option.
Altered spell school to Transmutation from Abjuration.
Added way to cast the spell without using the component, and a better version if you consume the diamond dust.