Mithril Magic

This variant goes one step beyond a Magic Point or Spell Point system to link those points to physical things: mithril, and it's various manifestations. In this magic variant spellcasters have to gather supplies with which to power their spells, whether that means purchasing them, slowly distilling their fuel from the environment, theft, or foraging. 

This variant results in less powerful spellcasters with limited resources, and slows the pace of play. It's most suitable for a game that's using slower rests (e.g., a 'short rest' takes place overnight, a 'long rest' requires a week or a campsite).

This variant to the classic 'Vancian' style of spellcasting in Dungeons & Dragons is intended to match the flavor and history of the Mura setting, but is easy to adapt into any home game, simply ruling that this is how magic has always been done. It can be used for PCs while leaving NPCs as they are for additional simplicity, or can be applied equally to NPCs with some simple math. The system is based on the Spell Points system (SEE Unearthed Arcana 3.5, or Expanded Psionics Handbook for similar rules), and so can benefit prepared spellcasters over known-spell spellcasters - however, with the change to the number of prepared spells a wizard or cleric can prepare in 5th Edition the power disparity is substantially reduced. 

Magical materials are where magic actually IS. You can use a tiny grain of mithril for each spell level. You can forage or buy it, or sift it from the water, etc. Mithril is found naturally in several forms, and produced in several more. It can be mined, reduced from mithril-rich wood, or collected from the sea in a concentrated salt. Mithril itself is a magically-infused silver, and when spent is reduced to a low-quality silver, often mixed with little bits of copper and tin.

One grain of mithril is the size of a grain of sand, and has a mass of about 2.65 mg. 1 gram of mithril is about 375 grains.

A single Magic Point - enough to power a 1st-level spell - is roughly equivalent to one gram of mithril.

Common denominations of mithril are:

A bar (50 grams, usually scored along the back to be split into fifty one-gram bits)

A coin (10 grams)

A bit (a one-gram nugget either made separately or broken from a bar)

A grain (375 grains to a gram, looks and feels like silver sand with a gentle glow)

One coin is about the same size, 1/50th of a pound or .32 oz, as a standard minted coin.

Other forms that the magical material takes are:

Aqua Mithra, or eitr, a solution of mithril dissolved in alchemical reagents. 250 mL (about 8 oz) is the equivalent of a coin, or 10 grams of dissolved mithril.

Mithril wood, which has veins of mithril running through it naturally. Typically only 1 gram can be recovered from 75 lbs of rich wood, but that means a single tree can have 25 grams or more (for a 2,000 lb tree, like a 50-ft. pine w/ 12-in trunk diameter).

Heartwood, the richest part of the richest trees, almost pure white and glowing. Heartwood can have as many as 1 gram per pound.

Mithrock, or mithril salt, is natural salt recovered from the ocean. Good mithril salt is about 10% mithril, so every pound of salt could be 'boiled down' into 45 grams or so.

Adamant, a mithril-infused diamond, is the most concentrated form of mithril. Some quirk of its lattice allows it to carry far more aether per gram than even pure mithril. An 'average' diamond (1 carat, or 200 mg/.2g) is equivalent to 100 grams of mithril.

Mithril sells for about ten times the price of platinum, so a single coin is 100 gp, a bar is 500 gp, and a diamond is 1,000 gold pieces.

 When a consumable spell component is required to cast a spell, typically an equal value of mithril can be substituted. This means, for example, arcane lock can use 25 gp worth of mithril dust rather than gold dust, an amount of 2.5g rather than half a pound (226 grams); or a casting of awaken can use 1,000 gp worth of mithril: a single 1-carat adamant diamond, rather than 1,000 gp worth of agate stones (about 1,500 carats, or 10 ounces of fine agate stones); and etc.

The reasoning behind the value of mithril is such: 

Unskilled hireling (min wage) - 2 sp is equivalent to around $50, so 1 sp = $25; so 1 gp = $250, so a 1,000 gp diamond is $250,000, where a mundane diamond, w/ mithril infusion, is worth $5,000, or the equivalent of 20 gp, or 6.4 oz of gold (real world for 6.4 oz gold is $8,320 on a 10-year average or something; so not too far off in value, gold is just 60% more common or devalued in Fantasyland).

In practical use, PCs are assumed to be able to collect a certain amount of mithril during each short or long rest, replenishing their supply of Magic Points with which to power their spells. At the end of each long rest a spellcaster makes a check, adding their spellcasting modifier and their proficiency bonus. The DC determines the success of the collection efforts:  check vs DC 10 for 1 grain (1 Magic Point's worth of material), DC 15 for 1d4, DC 20 for 1d4+2, DC 25 for 1d8+2, DC 30 for 1d12+3 or something. If this rate of recovery results in too grim & gritty a recovery rate (as it is substantially below the normal restorative rate of all of a character's MP) add the character's level and spellcasting ability modifier to the result. In this way a low-level character may restore 1d4+7 MP on a mediocre roll, enough for 3 2nd-level spells or so - closer to the standard rate of recovery. 

Characters may also be able to purchase or gather additional mithril throughout their travels, supplementing their natural restoration and foraging. 

With this model one issue that may arise is hoarding. How does one balance a spellcaster's power when they've stockpiled enough mithril to cast their highest-level spell slots dozens of times? The simple answer is that, like attunement slots, there are limits to the amount of raw magic a character can safely carry. Their maximum magical reservoir may be determined by their level, or a GM may choose to impose penalties - like wild magic surges once per hour - on characters foolish enough to carry around fistfuls of what amounts to magical uranium.