Interesting material types for fantasy resources/macguffins other than crystals or metals?

I always enjoy things made from the bones or other remains of powerful or uniquely magical beings/creatures.

Does it have to be materials? There’s only a finite number of types of elements and states of matter so you’re limited in what you can work with and one will look or be interacted with in roughly the same way regardless of what it is. I’ve seen lots of other ways beyond that as well. Bones and teeth and stuff have already been mentioned. But you can have people inhaling smoke, using powders to be mixed into a drink or sprinkled on people or things (pixie dust), drinking potions, drawing sigils or runes, etc..

Witch Hat Atelier makes it so there’s magic ink and you can do magic by writing or drawing with it. You can also imagine printing cards that can be drawn to do spells. Lots of actual real world religions have “amulets” that are knots of string or strings dipped in various kinds of dyes or spices that have certain significance, or sutras written or even embroidered onto paper. They can also have tattoos, which is something Full Metal Alchemist uses too.

Generally if you want spellcasting that’s more dynamic seeming you can do something like that. Maybe like, magic string that can have different effects based on knots you tie. Magicians duel each other by doing a cats-cradle type of game weaving their fingers around. Bones or teeth can work, maybe in some way imbued with aspects of the originating animal. Even in the real world fortune tellers claim to divine the future by casting bones and stones and analyzing how they fall, reading entrails of animals or the blood splatter of a bird that they kill, or looking at the patterns of tea leaves or coffee grounds. The presence of certain animals and appearance of clouds can themselves be omens.

There’s materials with some exotic properties as well, but once the material has exotic properties then the magic ends up being leveraging the behavior of the material as the interesting thing instead of randomly making it do unrelated magic. Take Ice Nine as an example. Or an even more mundane example, water is unusual in that it gets bigger when you freeze it but we don’t think of this as “magical.” Or mundane but still exotic example, iPhone batteries are secured to the frame with a special type of adhesive that loses its adhesion when a low-voltage current is applied to it and then becomes sticky again once the current stops. That’s magic if you ask me! Or what of fucking magnets!?

Even plastics as a building material used to be pretty magical. Much of what we use plastics for now used to be made of bone, ivory, or especially hard woods like ebony that had to be carved into shape. It’s laborious and there’s a lot of processing to prepare the materials and waste of material as you carve it off. Now we just have pellets that we melt down, inject into molds, and allow to harden meaning we can do it at insane scales.

There’s a lot about electricity that’s pretty magical seeming if you think about it. Microchips and PCBs are refined sand that can think based on the patterns of designs drawn on it. Some aspects of these designs can be modified by moving items around at the cost of having it be bulkier and heavier (FPGAs), and in other cases you can do stuff by adding material to modify the patterns (soldering). In olden days people used to do this by bottling lightning in a glass to guide it through a maze (vacuum tubes).

I feel like rocks are usually seen as the crusty dirty thing holding the magical crystal/ore, but what about treating rocks as an amalgamation of magic minerals instead?

Ferrofluids are cool. Fluids with magnetic iron that react strongly to magnetic fields.

"Fogs" have been used in interesting ways in fantasy, including resources.

Water itself is a pretty weird liquid if you wanna delve into its chemical aspects, maybe have something with more normal characteristics as that world's water to make water stand out.

Edit: crystals and metals are popular probably in part due to those being heavily studied materials in material science. There's a lot of weirdos in those. Like piezoelectric crystals that generate electric charge under pressure.

I think it's neat when the super powerful crazy object is just a sliver or refuse of some unimaginably powerful entity. Like the tear of some long dead god from hundreds of thousands of years ago in a vial gives you insanely ridiculous powers if you wear it on your neck. Or the eyelash of some ancient dragon that lets you breathe fire or something.

It makes your imagine run wild about how crazy the world must have been back then if someone is running around destroying armies with a tiny discarded sliver of a being that existed long ago.

Some inspiration, maybe, from The Elder Scrolls III: Morrowind (a great source of inspiration for all manner of Weird Fantasy, tbh):

• Chitin: insects have armor. If you have giant insects in your setting, then it's an obvious choice for your characters to, uh, "debone" them and use the segments of exoskeleton in protective clothing.
• Bonemold: in-setting, this is essentially a composite whose matrix is bone. Metal AF. There's a relevant in-game book series (CW: body horror).
• Ebony: neither a particularly dark-colored wood nor, as most in-universe characters believe, a volcanic compound (it's often described as a "glass", but it clearly behaves more like a metal, and there's another material which is actually called "glass" and is non-ductile); rather, it is the congealed blood of a god, left in deposits where it fell to the ground when his heart was ripped from his chest and thrown across the continent.

Wheel of Time has a fully synthetic material, cuendillar, formed with magic. It's something random powerful artifacts and buildings and other stuff from the distant past are made from, but the technique to make it was lost. Basically indestructible white glass.

Final Fantasy revolves around aether, which is more of an energy type (with several elemental classes) used as a component in things. Crystals are important because they can concentrate aether, but aether itself is everywhere. "This machine collects aether and will do a bad thing with it," is a pretty common MacGuffin.

I lean towards using organisms as a means of concentrating magical power. What @TheRtRevKaiser and @NaraVara said about bones: horns, teeth, bones, marrow and blood etc are the crystaliations of complex (organic) magical processes, with an aspect of Ancient Time, via sexually reproductive genetic inheritance and matrilineal mitochondrial inheritance. Progeny are essentially summons, gathered and developed with great effort.

And then there is the other traditional type: the intangible magical artifacts of words being powerful. In Frieren At Journey's End, they explore the concept that demons use words as a sort of magic against other races. By making sounds that resemble "help me" or "please, kill me if you must but spare my child", they can sometimes somehow avoid certain death.

Are you looking for scifi or fantasy?

For realistic stuff, scientists have recently observed "Time crystals", which is kind of like a perpetual motion machine down at the quantum level. Theres probably lots of cool things you could hypothetically do with that.

For fantasy, one of my favorite magic systems is in Final Fantasy X, where all magic basically comes from pyreflyes, which are little naturally occurring magic particles. When they are condensed they take on a material form based on the emotions or thoughts of people around them, so like a lot of negative emotions in one place will condense into a physical manifestation, and thats where monsters come from. Or people can intentionally craft them into spheres to use as magical tools.

Maybe I missed it but I didn't see mushrooms and rare plants.

I recently finished the Dungeon Crawler Carl series (currently available books) Dinniman writes many different ways to craft powerful items and you might find some inspiration there.

Real science answer:
aerogels - super light low density solids

One of the best SF writers for scientifically realistic applications of technology to future (especially space / terraforming) is Kim Stanley Robinson.

Fake (for now) science answer:

Nanotechnology - self-assembling, self-replicating molecule-scale machines - you could use them for morphing weapons, self-repairing armor, even force fields, but those are the "boring" answers. Probably more interesting to think about the offensive and defensive applications of them invading a body / fighting off invaders. If you imagine them doing things like rewriting DNA, altering physiology, maybe even affecting mental processes, then they start to become more like spells.

Raven, a character in Snow Crash, does some interesting things with plain old glass.

...sentient kombucha with psychic abilities...

Flubber fits all the criteria to a T.

The best answer here is to pick something absolutely mundane, then find a justification for it to be magical.

A glass of milk? This bottle came from before written history. You know the phrase “milking it for all it’s got?” This milk is the result. This milk is all we have. I sure don’t know what that means, but it sounds powerful.

A plank of wood! At the beginning of the world, a divine being planted a single tree. People then took shoots from that tree and grafted them onto all sorts of standard trees. Each piece of wood from these half-divine trees has a special property - cherry tree wood compels people to tell the truth. Ash makes you resistant to fire. Maple makes you ravenously hungry.

The more boring a thing is to begin with, I think it makes the answer to “well, why would anyone care about it” more compelling!

Synthetic polymers, maybe? I just read a bunch of spoilers about Project Hail Mary, and apparently some exotic polymers come up as a plot point. In the modern era, we can synthesize materials that're nearly as "strong" as aluminum, can withstand hundreds of degrees celcius, or that are so slick that nearly nothing can stick to them. We can form them into films and make balloons to reach the high atmosphere, or layer them into hard shells to reach the depths of the ocean (a few times before imploding). Not sure how you'd work that into a fantasy setting, though 😅

Carbon nanotubes are a common sci-fi trope which might work as well?

Antimatter. Since CERN can now put antiprotons in a truck and drive them around, it might not be completely the province of fantasy, bit it is an amazing material for a Macguffin, as it was in several embodiments for Alastair Reynolds Revelation Space.

Come on, people, there's only one suitable answer relevant to our era: information.

Yup, just like Keanu in Johnny Mnemonic, an info courier is tasked with manually transporting data in his brain that's too sensitive for transmission on the internet. Like say, a world where metal detectors forbid people from carrying around phones and personal computers, so indentured IT workers get around it by uploading computer viruses to their brains used to infect independently siloed AIs. Except this time, the virus is contagious to humans...

A symbol/configuration, but only where it occurs in nature?
Sap?
Lymph?
A rhythm or melody?
A harmony of multiple tones?
A memory?
A mechanism?

Just some thoughts.

What about Ley Lines? Magical energy coursing through the earth like rivers unimpeded by anything physical. The closer you are to one, the more power available.

If you're looking for plot ideas: the Ley Lines could shift en masse, throwing the world order into chaos as cities dependent on the magical energy are suddenly without; magic users can temporarily shift the smaller ones to them to power spells, but a nasty mage has discovered they can pull major ones to them; or an entity acts as a Ley Line "sink" (like putting your hand on top of a plasma globe), but can't use magic themselves, just off the top of my head.

In the Locked Tomb Series, necromantic powers are fueled by the release of both life and death energy upon killing people and even planets.

Had an idea for a setting for a magical mall, where all of the merchandise lives up to the advertised abilities. Blenders would blend anything, snake oil will cure your ailments and toy laser beams can put a hole in the wall. Everything would mostly be manufactured the same way, but in theory, as long as it came from within the mall, someone could take a cardboard box, take it into an arts and craft shop, then make whatever they wanted.

"The Death Mirror". Every time you kill someone while looking into their eyes with complete empathy, uttering an incantation, you capture all the magical energy that person would have in their remaining, natural lifetime. Of course, the Death Mirror will eventually drive you mad, as, in a way, you have died many times. You experienced fully the deaths of everyone you killed, as if you were them.

"Serendipity". Every time two friends meet randomly after a long time. Every time a great discovery happens by accident. That is not really "random". I mean, it is, but there is an order to Serendipity. You learned to find it. You also learned how not to find it. Because, you see, looking at Serendipity instantly disolves it. You must be walking in a sure, carefully planned direction, at the same time that you have no idea where you're going and why. Serendipity is an "additive" phenomenon; it brings something into reality that did not exist before. The interactions between these elements generate a lot of magical energy. You are far from understanding its mechanisms, but you are an expert at sucking all the delicious juice of Serendipy from whoever has experienced it. At that time, all feeling of warmth and wonder is lost in the room. Any bond or discovery is forgotten, never to be found. It is just a regular place now. Little by little, you're making the world more backwards and dull. But at least you are not killing anyone. Besides, how much harm can just one little mage do anyway?

One of the coolest magical schemae I've seen was in Greg Bear's Songs of Earth and Power duology (The Infinity Concerto, The Serpent Mage). It involved a a couple of media not often considered...

I'm also a sucker for bio- and nano-tech that's nearly indistinguishable from magic. Ian McDonald's The Broken Land (UK title, With Hearts, Hands, and Voices) has people with the genetic endowment to communicate with and craft pseudoflesh into living structures, creatures, and tools of considerable power.

Tim Powers' Last Call has a mythology built around a card game.

Then there's Charles Stross' Laundry Files series, where getting enough mathematics and computational power in one place lets Things happen.

And another one - Yoon Ha Lee's Machineries of Empire series uses mathematics based on calendar systems to work magic that powers stardrives and weapons. Changing a planet's calendar aligns it with the Imperial magic system, and conquest reinforces the Empire's power.

Forgot to include Kameron Hurley's Apocalypse Nyx series. It's grimdark biopunk, with magic materials environmentally limited to mutated bugs and animal or human flesh for the most part. The distinction between tech and magic is blurry in the sense of Arthur C. Clark's quote. The series has a well-paced and written storyline of action, adventure, politics, and bloody mayhem. The "magic" system might have some of what you're looking for.

Dune uses the spice melange, a highly addictive drug which among other things enables humans to navigate in outer space without computers and is the source of Paul Atreides' prescience. Because it's essential to space travel (in a world that has banned the use of machines that think like humans) and only found on Arrakis, it's the cause of a lot of political scheming and basically the whole plot of the series.

In the real world, mind altering substances have been used for religious rituals here and there to bring people closer to the truth, the gods or whatever. In a fantasy setting that could literally be the case.

Mistborne is the first thing that comes to mind since that's basically the hook. Find new metals, get new powers, do new degenerate things. They have several "secret" metals but i'm kinda keeping things vague since it gets spoiler heavy FAST. Some of them are real world metals/alloys, others....less so.

This is a question that could go down a number of rabbit holes in the halfbakery. I'll suggest a couple tried and true options: pykrete and oobleck.

There's some great answers here, and like the other user my thoughts went straight to Morrowind, but also to mythology.

• Silk, or the silk of specific bug — in TES3 silk clothing is a lot more enchantable than cloth, leather, or metal. In-game it's used as a justification for mages not wearing armor and to create a higher equipment tier for magic users.

• Milk, or honey, or the product of a specific animal — Robin McKinley's Chalice has a system where magic centers around roles and talismans, and where most chalice-bearers use wine, the protagonist happens to be a beekeeper, sooooo

• the soil of one's birthplace — the most obvious example is vampires, who need it to restore themselves, but mages who are rooted in place (or can only leave by taking a chunk of bedrock, or gallon of lake water, and so on, with them) are a minor trope already. See also ocean water a la Black Panther 2

• personal crafting — a lot of magic systems (and mythology) feature magical items that are created by either self-sacrifice or self-mutilation. An item worn continuously for years that takes on it's bearer's power (and sometimes personality). Sages or Liches who put their own souls into an artifact or phylactery or horcrux; more impactful when the soul is torn or split during the process, sometimes. Magi who filter their spirit or consciousness or personal energy through a device or item or weapon over and over, charging it with power over time. Wands made from the user's own bones. Potions or dyes made from the user's own blood or tears. Clothing made from the wearer's own hair.

• Items soaked in cosmic energy — water from a pool that reflects the full moon, ice that froze before the sea became salty, ancient materials lying undisturbed for aeons. Happens sometimes in scifi, too: RA Heinleins sunstones were what made me think of this category.