There are several spells that use rubies, generally by crushing them.
Continual flame uses 50GP of ruby dust. See Basic Rules, pg. 227
A flame, equivalent in brightness to a torch, springs forth from an object that you touch. The effect looks like a regular flame, but it creates no heat and doesn't use oxygen. A continual flame can be covered or hidden but not smothered or quenched.
Simulacrum uses 1500 gp of powdered ruby. See Basic Rules, pg. 276
You shape an illusory duplicate of one beast or humanoid that is within range for the entire casting time of the spell. The duplicate is a creature, partially real and formed from ice or snow, and it can take actions and otherwise be affected as a normal creature. It appears to be the same as the original, but it has half the creature's hit point maximum and is formed without any equipment. Otherwise, the illusion uses all the statistics of the creature it duplicates, except that it is a construct.
Forbiddance uses 1000 gp of ruby dust. See Basic Rules, pg. 243
You create a ward against magical travel that protects up to 40,000 square feet of floor space to a height of 30 feet above the floor. For the duration, creatures can't teleport into the area or use portals, such as those created by the gate spell, to enter the area. The spell proofs the area against planar travel, and therefore prevents creatures from accessing the area by way of the Astral Plane, Ethereal Plane, Feywild, Shadowfell, or the plane shift spell.
Forcecage uses 1500 gp of ruby dust. See Basic Rules, pg. 243
An immobile, invisible, cube-shaped prison composed of magical force springs into existence around an area you choose within range. The prison can be a cage or a solid box, as you choose.
Sequester, see Basic Rules, pg. 274 also uses ruby dust, using
a powder composed of diamond, emerald, ruby, and sapphire dust worth at least 5,000 gp, which the spell consumes)
And does this.
By means of this spell, a willing creature or an object can be hidden away, safe from detection for the duration. When you cast the spell and touch the target, it becomes invisible and can't be targeted by divination spells or perceived through scrying sensors created by divination spells.
Infernal calling and Summon Fiend also use rubies, but your ruby isn't valuable enough.
You could also arguably use them for magical crafting, or use them for bribery or social things.