Mineral MacGuffin

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"1-Up: Great job, Stinkoman! You got the Green Crystal Shard!

Stinkoman: Will we ever find all the colors before the bad guy?"

- Homestar Runner

A long time ago, several magical items were created. What were these amazing planet-destroying-if-ever-found-by-the-Big-Bad artifacts? Jewels, of course! They're shiny and glowy, and geometric, and crystalline. And let's not forget the allusions to wealth and regency.

Every super powerful Plot Coupon has to be a diamond or gem of some sort. Bonus if it's been somehow shattered into easily re-assembled pieces. And you, our heroes, in all likelihood Gotta Catch Em All. Bonus bonus points if there's a Full Set Bonus. Or just the one in the case of the Crystal Prison. If there are more than one gem, they'll usually be conveniently Colour Coded by their Elemental Powers, although sometimes they're only different colors because it looks cool.

That is, cut and polished Green Rocks. You can even slap them on just about anything to give them a power boost... or just to look neat!

Note that while Added Alliterative Appeal made the name of this trope inevitable, many examples of this trope aren't actually MacGuffins because they serve a real purpose beyond being the object of a quest. They might not even be made of minerals in the case of Body to Jewel, and the purpose may be exposition in the case of Data Crystal.

There's probably an entire subtrope one could write for plots in which it turns out the villain wants a jewel not for its monetary value, but because it's necessary to focus the beam of a giant frickin' laser. Such gems can even be plucked straight from a mine wall and put into said laser thanks to their All-Natural Gem Polish.

Anime & Manga

 * Sailor Moon is absolutely flooded with both good and evil jewelry, the most famous being the Silver Crystal (which had to be assembled from 7 Rainbow Crystals in the anime). Most of the jewelry is, oddly, physically manifested aspects of the human soul. Any given person apparently has a friggin jewelry store in there somewhere.
 * The Ruby and Sapphire Orbs from Pokémon.
 * As well as the various evolution stones.
 * One ancient and powerful jewel is the Shikon Jewel (shikon no tama or "Jewel of Four Souls" in the dub) from Inuyasha. It shatters early on, setting in motion the Gotta Catch Them All plot.
 * The Jewel Seeds from Magical Girl Lyrical Nanoha.
 * The Prism Stones in Futari wa Pretty Cure.
 * The pearls in Mermaid Melody Pichi Pichi Pitch.
 * The Star Crystal in Negima!?.
 * Princess Tutu. The titular princess gathers shards of (which conveniently look like shards of a jewel) then finds out that the last shard is
 * The Jewel of Life from Ronin Warriors.
 * The eponymous Dragon Balls.
 * The Philosopher's Stone from Fullmetal Alchemist.
 * Sakuradite in Code Geass. Though it has most of the functional properties of weapons-grade uranium, it's played more like oil in the Middle East. It powers most everything in modern society, including the Knightmare Frames, and it's worth invading a country over.
 * The Moonstone from Kimba the White Lion.
 * Dualium in AKB0048 which serves as the reason why entertainment is banned.

Comics

 * The Infinity Gems from Marvel Comics.

Films -- Live-Action

 * Although non-magical, the Heart of the Ocean was the elusive MacGuffin that kicked off the framing story of James Cameron's Titanic.
 * The Unobtainium (no, seriously, that's what it's called) in Avatar is actually more of a Mineral MacGuffin -- aside from being a source of Human-Na'vi conflict, its only use is to sit there and be expensive.
 * In the various wikis and other supplementary sources, it's revealed that the element, though not a fuel source per se, is vital to the operation of interstellar vehicles -- in other words, it's an oil allegory.
 * El Corazon ("The Heart"), an enormous emerald in Romancing the Stone.
 * Subverted in the sequel, Jewel of the Nile, which sounds like a Mineral MacGuffin, but is actually... a person.
 * The "Blue Water" sapphire in the 1926 and 1938 adaptations of Beau Geste.
 * The eponymous stone from The Dark Crystal, as well as the shard that must be reunited with it. Unusually, both shard and Crystal aren't cut gemstones, but hunks of rough crystal in its natural state.
 * In Joe Versus the Volcano, the reason Samuel Graynamore sends Joe on his journey is to bargain for a rare mineral called Boobaroo, needed in his manufacturing industry.
 * The titular Blood Diamond
 * The film Cash revolved around stealing three diamonds owned by three different people. Since they were cut from one original stone, together they provide a {full set bonus}.

Gamebooks

 * In the Lone Wolf gamebooks and spin-offs, there are several Mineral MacGuffins. First and foremost is the Moonstone, a powerful artifact crafted by a race of demigods, the Shianti. So important it is in Magnamund that year 0 on this world's calendar is set on the date of its creation. Then, there are the Lorestones, made by Nyxator the Dragon, which spun the Gotta Catch Them All plot of the whole Magnakai series. Even the villains have their own set, the Doomstones created by Agarash the Damned, which any hero is better off destroying on sight.

Literature
"The red heart of the night it is, strong to save or to damn. It came from afar, and from long ago. While I held it, none could stand before me. But it was stolen from me, and Acheron fell, and I fled an exile into dark Stygia."
 * In Chivalric Romances, the magical jewel that shone of its own light is a stock magical item.
 * The Silmarils from JRR Tolkien's The Silmarillion, and to a lesser extent, the rings of the Elves, which are set with diamond, sapphire, and ruby.
 * And the Arkenstone from The Hobbit, which is only notable in the story because Thorin wants it.
 * Odd take from the Kid Lit fantasy series Diadem: All gems were magic and each had their own power, but only someone with magical talent could unlock them.
 * The Sun Stones from the Dinotopia books, used to power the strutters.
 * The Orb of Aldur and its evil counterpart, the Sardion from David Eddings' Belgariad and its sequel series, The Malloreon. Individually they're both quite powerful. If any one person (or being) can manage to hold both of them, it would become a god. Literally.
 * Eddings' Elenium has another another sapient (and almost as powerful) blue jewel, The Sapphire Rose (or Bhelliom), at the center.
 * The gems of the Belt of Deltora in Deltora Quest.
 * The more powerful and plot-important gelstei crystals in Ea Cycle, especially the gold and silver varieties.
 * Lampshaded brilliantly in the extremely Genre Savvy fantasy novel Villains by Necessity, with the Spectrum Key: a spherical crystal worldgate broken into six identically-sized pieces in six different colors, each hidden in a different location by a different Hero and protected by a different clever trap. Several characters comment on the colors; one character is from a colorblind species and can't understand what they're blathering about.
 * The "Blue Water" sapphire in Beau Geste (1924).
 * In Robert E. Howard's Conan the Barbarian story "Jewels of Gwahlur", the Teeth of Gwahlur.
 * The Elephant's Heart in "The Tower of the Elephant". There are also a number of glowing gems that they ignore for the real thing.
 * The Heart of Ahriman in The Hour of the Dragon.

"Above all, why had Ka-nu shown him the green gem of terror, stolen long ago from the temple of the Serpent, for which the world would rock in wars were it known to the weird and terrible keepers of that temple, and from whose vengeance not even Ka-nu's ferocious tribesmen might be able to save him?"
 * In Robert E. Howard's Kull story "The Shadow Kingdom" the stolen gem.


 * In Robert E. Howard's Kull/Bran Mak Morn story "Kings of the Night", the jewel in Bran's iron crown.
 * Subverted in an Artemis Fowl mini-book that takes place between the first two novels. Artemis goes to a lot of trouble to steal a unique jewel from a group of dwarves pretending to be a human circus troupe. He gives the stock "focus a new laser I'm developing" excuse to dwarf ally Mulch Diggums, who seems sceptical but doesn't push it. Artemis really wants it as a present for his mother, since it matches the colour of his missing father's eyes.
 * In Alan Garner's The Weirdstone of Brisingamen, the titular gemstone is part of a magical bracelet that can be used to protect its wearer, but serves a more important purpose in powering the enchantments which keep Arthur and his Knights agelessly asleep in Fundindelve.

Live-Action TV

 * Power Rangers is quite fond of this. The Power Crystals in season 1, the Zeo Crystal(s) in seasons 3 and 4, the Trizerium Crystals in season 9, the power orbs (that give the user control of a Wild Zord) in season 10, the Dino Gems in season 12, the jewels of the Corona Aurora in season 15...
 * In Doctor Who, there was a season-long storyline involving the search for all the pieces of the Key to Time.
 * Later, in one of the specials, a perfectly ordinary diamond becomes one of these when.
 * The magical and sometimes mischievous Stone which changed hands several times in The Wanderer.
 * How many times did various Star Trek series base a plotline on the ship running out of dilithium crystals, exactly? Dozens? A hundred?

Radio

 * A mundane version occurs in Adventures in Odyssey when Dr.Blackgard tries to gain the minerals buried under Whit's End that he needs to produced a supervirus.

Tabletop Games

 * The Heart of Paradise in the Magi Nation card game.

Video Games

 * While it doesn't have gemstones, portions of the plot of Ace Attorney: Trials and Tribulations revolved around Dahlia's heart-shaped bottle necklace.  Its eventual fate?
 * The eight elemental crystals from Mardek RPG. Each of them is is the font of all energy of their type: aside from the basic elements, the Light and Dark crystals are responsible for Good and Evil, the Fig crystal for all thoughts and dreams, and the Aether crystal for all souls and lifeforces. Every planet has its own set, although non-life-bearing planets don't need the Moral or Spiritual ones.
 * Besides the Chaos Emeralds from the Sonic the Hedgehog series, there is:
 * The Time Stones from Sonic CD.
 * The Super Emeralds from Sonic the Hedgehog 3.
 * The Master Emerald from Sonic and Knuckles onwards.
 * The Sol Emeralds from the Sonic Rush Series.
 * The Chaos Rings from Knuckles Chaotix.
 * The Precious Stones from Sonic Shuffle.
 * The World Rings from Sonic and The Secret Rings.
 * The Crystal Stars from Paper Mario the Thousand Year Door, and an honorable mention to the pieces of Star Road from Mario RPG, which at least look the part.
 * Any Final Fantasy game involving crystals. The Huge Materia count.
 * In Final Fantasy IX, the summoning doodads (which are implied to look like regular gemstones) get considerably more play than the traditional Four Crystals also in the game.
 * Final Fantasy XII has nethicite, which is capable of causing Earthshattering Kaboom|s (and therefore the perfect deterrent)
 * The Legend of Zelda has a bunch of these, usually in the colours green, red and blue to represent the Goddesses and their respective powers (courage, power and wisdom). A Link to The Past has the three Pendants of Virtue; Ocarina of Time has the three Spiritual Stones; The Wind Waker has the Goddess Pearls; Phantom Hourglass has the Pure Metals. The Legend of Zelda Four Swords, The Legend of Zelda Four Swords Adventures and The Minish Cap all feature the four Elements/Royal Jewels.
 * Freshly Picked Tingles Rosy Rupeeland's entire gameplay revolves around getting as many rupees as possible--including the Super Rupees that act as the games dungeon counters and the final Master Rupee.
 * The Moon Crystals in Skies of Arcadia.
 * The red stone in Shadow of Destiny.
 * The four Elemental Stars in the Golden Sun series.
 * Null Crystals from zOMG. Their exact origin hasn't been explained yet, but they do seem to have enormous power. Null Crystals have the power to neutralize G'hi energy, forcing The Animated to avoid them at risk of de-Animation. The crystals come in three varieties.
 * Null Fragments are used in Item Crafting, and are Handwaved as the reason why some recipes use rather illogical ingredients.
 * Transit Crystals are large crystal outcroppings that can repel and de-animate The Animated. When touched, they can teleport a person to its partner crystal, assuming that they are attuned to it. They're used to send people to the Null Chamber.
 * The Null Chamber serves as zOMG's hub. It is filled with "Dark Crystals", which have the power to neutralize G'hi energy, allowing players to swap out and charge rings. In addition, the Null Chamber grants anyone who enters it a form of immortality. If you are killed in the field, you can release your lifeforce and reform at the Null Chamber.
 * Somewhat used in Paul's chapter of Eternal Darkness. Three gems, a ruby, a sapphire, and an emerald, are needed to open catacombs within a church and proceed through the level -- they seriously are just plain gems, though, with no power of their own. Their color does seem to hold some significance with the game's unique element system, however, depending on where they're found. Green represents sanity and the emerald is found in the staff of a priest depicted in a wall carving, and Paul's own staff is used for sanity recovery. The blue gem, blue representing magic, has to be taken from a Horror, a hulking monster that fires bolts of magic from a distance. The last gem is taken after a miniboss fight with a 600+ -year-old and very zombified Anthony. Defeating him allows you to take his Woobie - pardon me, ruby eye, red representing strength.
 * Kirby 64: The Crystal Shards. The titular crystals were all pieces of an even bigger crystal.
 * The Atlamillia from Dark Cloud. There is just one in first game, and it functions as a tool exclusive to the hero. In the sequel, they are three Cosmic Keystones that enable Time Travel and grant godlike power to anyone who collects all three. Note: it is a very bad idea to actually collect all three. Very bad. Lousy Ancients and their failsafes...
 * A more traditional kind of MacGuffin is found in Dark Cloud 2: the mineral known as zelmite. In the post-game chapter, Max ventures into the Zelmite Mine beneath Palm Brinks merely to go and fetch some of it as fuel for the Blackstone One.
 * Refractors in the Mega man Legends/Rockman Dash series are big crystals left over from an earlier civilization. Small ones serve as money, big ones power airships.
 * Practically all gemstones in Fate have magical powers, except the Lampshadingly-names Gem of Lost Hopes.
 * In Pokémon Platinum, the Red Chain. To be fair, however, it WAS bloody difficult and ended up not working in the end. Cyrus essentially However,  . Man,   did a good job at setting up that failsafe.
 * Hell, the ~Pokémon~ games themselves could be considered Mineral MacGuffins to die-hard collectors. You've got Gold, Silver, Crystal, Ruby, Sapphire, Emerald, Diamond, Pearl, and Platinum. Of course, this is averted by the fact that the games aren't actually made of these materials...
 * In Ruff 'n' Tumble, the big bad needs marbles in order to power a world-domination machine.
 * The entire backstory for Torchlight revolves around the discovery of a mine with a rich seam of Ember.
 * They are more than just bling in Tail Concerto.
 * The PC game Jazz Jackrabbit 2 had the titular character trying to get back the diamond from his fiancée's (the princess's) wedding ring--an enormous diamond the main villain was using to power his time machine so he could erase rabbits from history.

Web Animation

 * Spoofed on Homestar Runner with a mention of "Stinkoman and the Challenge of the Crystal Shards" (at the end of this cartoon).

Web Comics

 * Soulstones, found in the Earthsong 'verse, formed of semi-sentient minerals which make up the consciousness of planets (read the comic, it's much clearer there) crystallise out of characters' blood INSIDE THEIR CHESTS. If not dealt with correctly by teleporting the relevant character to Earthsong, they then proceed to spontaneously explode.
 * El Goonish Shive has the Dewitchery Diamond, a huge green diamond that is responsible for creating one of the main characters.
 * Wayward Sons: The Star Core brought the protagonists and antagonists to earth, and empowered them. It's currently set in the hilt of Suras' Cool Sword.

Web Original

 * Super Stories features the Trabethan Jewel, a large jewel with the ability to amplify various kinds of waves. Its adaptability has made it the focus of many a failed doomsday weapon, and it is thus usually sought by somebody and spends most of its time in police evidence lockers.

Western Animation

 * The Reality Gems from Danny Phantom, a homage to the Infinity Gems from Marvel above.
 * The Thirteen Treasures of Rule in Pirates of Dark Water.
 * Energon in Transformers: Beast Wars and Transformers Energon (it appeared in the original series as a liquid rather than a solid).
 * In Transformers Animated, the Allspark starts out as just a box o'endless power. However, after it shatters the fragments manifest as crystal shards.
 * Three episodes of My Little Pony have three different gems: The Sun Stone ("The End of Flutter Valley"), the Flashstone ("The Ghost of Paradise Estate"), and the Heart Stone ("Crunch the Rockdog").
 * Also in the recent remake My Little Pony Friendship Is Magic where The power to defeat gods and god-like entities can be wielded by those attuned to the "Elements of Harmony", artifacts traditionally depicted as six gemstones. Since the elements were re-activated by the main characters, their powers have been stored within 5 jeweled necklaces and one Big Crown-Thingy.
 * Spoofed in Duck Dodgers in the 24th and a Half Century. Duck Dodgers and Marvin the Martian end up destroying the entire planet in their attempt to claim the last remaining supplies of Illudium Phosdex, the shaving cream atom.
 * Tenko and the Guardians of the Magic has 16 different sorts of "Starfire Gems", which are kept in a tenko box. They give powers to whoever owns them.
 * ThunderCats (2011) has the Eye of Thundera, an Amplifier Artifact and Power Crystal for the Sword of Omens

Films -- Live-Action

 * The diamonds needed by Mr Freeze's for his frost-beam in the film Batman and Robin.
 * The James Bond film Diamonds Are Forever, where the only reason Blofeld set up the diamond-smuggling pipeline in the first place was to snag enough gems to power his Kill Sat's Frickin' Laser Beams.
 * One of the Pink Panther films used the eponymous Pink Panther diamond for this.
 * Dr. Claw uses a giant ruby as part of his time-freezing beam in Inspector Gadget 2.
 * Through the majority of Congo the blue diamonds are wanted for laser communication with satellites. The last few minutes subvert this when the main character when said laser gets turned Up to Eleven and  This was a spur of the moment solution, thus the diamonds maintain their MacGuffin status up to that moment.

Literature

 * Subverted in a short story in The Artemis Fowl Files: Artemis claims to want a blue diamond for a laser he's building, but at the end of the story it turns out

Gamebooks

 * In some endings of the Choose Your Own Adventure book Mountain of Mirrors, you can use a huge diamond to focus sunlight on the ice pillar that supports a gigantic frozen cavern, melting it away and collapsing the roof on a monstrous army.

Live-Action TV

 * The Doctor Who episode "Tooth and Claw". In this case, it's the good guys who want it, to create a moonlight laser to overload a werewolf. It being the very real Koh-i-Noor diamond.
 * Done before in the episode "Horror of Fang Rock".
 * Done in Power Rangers RPM, where they need a specific black diamond owned by the yellow ranger's family.
 * Done in the original Knight Rider, where an experimental laser focused with a black crystal is stolen and weaponized. And it could've taken out KITT, except that Bonnie developed a spray-on deflective coating.

Video Games

 * Sonic Adventure 2, in which Eggman needs the Chaos Emeralds to power the Eclipse Cannon.
 * Eggman does this again in Sonic Unleashed, where he uses Super Sonic to suck the Emeralds' power dry in order to power the Chaos Energy Cannon and shatter Earth into pieces, releasing Dark Gaia from within. It gets better as you go through the game.
 * Not unsimilarly, Crash Bandicoot 2 sees Cortex trying to get his hands on 25 crystals to activate his brainwashing device, while Nitrus Brio wants the 42 gems to blow up the aforementioned device.

Web Comics

 * Done by the villain in the first story arc of the webcomic Amazing Superteam.
 * The Inexplicable Adventures of Bob has borfomite, which when combined with caramel can power a gun to make things explode real good. Also, Galatea used a stolen French ruby to focus the laser of her hologram gizmo.
 * In Strays Meela finds one.
 * In Endstone, the title stone and others -- the Toadstone, the Dragonstone, etc. -- can be "rocked" by those with the talent and produce powerful magic.

Western Animation

 * Done in the Five Episode Pilot of Chip 'n Dale Rescue Rangers.
 * Likewise the pilot of Tale Spin, where the gem produced unlimited amounts of electricity instead of focusing it.
 * A similar plot happens in The Powerpuff Girls. At least twice, and probably several times.