Crystal is a popular material in fiction. Maybe because it's exotic, maybe because it's mysterious... or maybe just because it looks really cool.
Whatever the reason, it's common for important or magical items to be made out of crystal, and for these items to be used as normal despite crystals being essentially very pretty giant rocks. (And yes, we know that the scientific definition of crystal is broader than that and that among other things, snowflakes are also technically crystals, but the word colloquially only refers to the varieties of rock and 99% of the time the rocks are what are pictured when something is described as crystal.)
This leads to odd situations like a character swinging around a crystal sword without a care for its logically enormous weight or of the fact that there's a reason that rock weapons are very uncommon: they can be snapped very easily if pressure is put on their sides. Chalk the prevalence of these sorts of weapons made up to Rule of Cool (and don't even get us started on crystal bows...)
- Based on the 1982 Remco action figures, Marvel's 1983 Saga of Crystar comics had main characters Crystar and Warbow uses a crystal sword and crossbow respectively. These characters would return again in the 2010s with Marvel's Weirdworld miniseries.
- In The Wheel of Time, the crystal sword Callandor is a major symbol of the Dragon Reborn, and is an indestructible Amplifier Artifact of terrifying power for good measure. Oddly, its design was deliberately flawed in ways that make it dangerous to wield and enable it to channel the Dark One's own power against him.
- The Fighting Fantasy gamebook Creature of Havoc includes a crystal club that can defeat any enemy with one blow but shatters after being used. It happens to be the only way to defeat the Big Bad by destroying the portal to his Pocket Dimension.
- Silver on the Tree. Will Stanton and Bran journey to the Lost Land to retrieve the crystal sword Eirias, which is necessary to fulfill the prophecy of the destruction of the Dark.
"And where the Midsummer Tree grows tall, by Pendragon's sword the Dark shall fall."
- The Elric Saga story "To Rescue Tanelorn". The Olab are reptilian creatures that wield large clubs. The clubs have discs a foot in diameter made of crystalline rock embedded in them. The Olab swing their clubs to fling the crystal discs at opponents.
- In the science fiction Liaden Universe, protagonist Val Con has a crystal knife made on an alien world by the Knife Clan of Middle River, which is nearly indestructible and has an Absurdly Sharp Blade. The Knife Clan is said to grow the blades in caves over a period of decades, with considerable care and attention required for them to come out with the required characteristics.
- Adrienne Martine-Barnes wrote a series of fantasy novels revolving around four Cool Swords, the second of which was the Crystal Sword.
- Dune: The Fremen wield "crysknives" ground from the crystal teeth of Sandworms. Each is considered a holy weapon that shouldn't be shown to outsiders and mustn't be sheathed without drawing blood — and is an Absurdly Sharp Blade to boot. Curiously, crysknives will disintegrate when separated from a living being's presence unless "fixed" to prevent that.
- A Song of Ice and Fire: The Others, fae beings that embody Evil Is Deathly Cold, wield Absurdly Sharp crystalline blades that hold a faint blue glow and can shatter steel with their chill. Word of God is that they're transmuted ice.
- Dungeons & Dragons:
- Weapons can be forged from "deep crystal" that's as hard as steel and can channel the user's Psychic Powers to deal extra damage.
- The Thri-Kreen (or Mantis Warriors) are known to use thrown weapons and polearms with the blades made from a crystalline substance called dasl. Its origin is closely guarded secret, and a mystery for other races. The Dark Sun supplement Thri-Kreen of Athas reveals that dasl is created by mixing the thri-kreen's venomous saliva with sand.
- Stormbringer/Elric!. Olab throw crystal disks at their opponents using a club-like launcher.
- In Diablo II, a Crystal Sword is a fairly basic, low-leveled weapon that's rather frail. It's one of the first weapons that has six sockets available for buffs or other magical effects to be added on to it though, making it somewhat popular for strategies involving magic or runes.
- Dungeon Siege has a set of mid-high-level crystal equipment that includes plate armor, greaves, gauntlets, and a helmet, as seen in this image◊. There is also a much lower-leveled crystal bow.
- Tibia has the Crystalline Axe, which is made of red crystal for a blade and is one of the strongest one-handed axes, the Crystal Wand, which is obtained via quest, the Crystal Sword, a weak weapon for beginner knights, the Crystal Crossbow (and Crystal Arrows), a powerful weapon for high-leveled paladins, and the non-usable quest item the Crystal Cannon.
- RuneScape has an entire set of crystal weapons and armor. They slowly degrade from taking hits, but wielding attuned ones in both hands means the player deals bonus damage.
- Crystal weapons in Dark Souls I are extremely powerful but have low durability and cannot be repaired by any means. Like most things crystal in the game, they are ultimately products of Duke Seath the Scaleless' research, who also invented several sorceries that temporarily turn regular weapons into crystals.
- Recettear: An Item Shop's Tale has a Crystal Sword, which is "forged of pure crystallized energy".
- In Minecraft you can make diamond weaponry and armor, which is quite powerful.
- Space Empires V uses a sci-fi variant; accessing the Crystallurgy branch of the Tech Tree will allow you to build spacecraft fitted with crystalline armor and armed with crystal shard torpedoes.
- A Very Long Rope to the Top of the Sky may have crystal weapons with its Saecelium series of weaponry. Saecelium is known as a type of crystal, but the weapon's themselves are never physically described, and there's an official Shrug of God as to whether they're pure crystal or just be metal with Saecelium incorporated into it or something.
- Dungeons & Dragons Online has a two-handed crystal sword named Terror, which can cast a spell three times a day, has the ability to inflict the "Nightmare" status condition on enemies, and forces opponents to roll a save against fear when it's used against them.
- Final Fantasy has various Crystal armaments and armour throughout the series, typically as a sword but sometimes as other weapons.
- In The Bard's Tale Trilogy, diamond weapons are the strongest equipment you can buy from a store. While they'll be outclassed by enchanted items you might find, because class-based equipment restrictions they continue to be useful to the end of the game.
- Avencast: Rise of the Mage: Magic Staves come in a wide variety of materials, including solid diamond. Given that one of the magical disciplines uses the staff extensively as a melee weapon, it's fortunate that the game uses Unbreakable Weapons.
- Doctor Thaddeus Dare is The Villain of the Loonatics Unleashed episode "Going Underground." Doc Dare steals the Jade Scorpion crystal, with which he pulls entire precincts of Acmetropolis into his subterranean domain. At one point, he draws raw power from the crystal into his Boom Stick, from which he launches a Death Ray at the heroes.
- The main character, many of the protagonists and all of the antagonists of Steven Universe are living crystal beings who not only use crystal-based technology and weaponry, but for a good part may be considered living weapons themselves.