Crystal

• Type: Magical Material; Divination Tool; Container
• Primary Uses: Scrying, Storing Memories, Storing Potions
• Notable Forms: Crystal Ball, Crystal Phial, Crystal Goblet

Crystal is a transparent mineral highly valued in the wizarding world for its purity and its ability to channel or remain inert to potent magic. Its primary magical application is in the art of crystal-gazing, a branch of Divination, where it is used as a medium to see into the future or gain insight into distant events. The clarity of the crystal is believed to be essential for focusing the Seer's Inner Eye. Beyond Divination, crystal is prized for its non-reactive and durable nature, making it the ideal material for crafting high-quality containers for sensitive or powerful magical substances. These include memories extracted for use in a Pensieve and rare or volatile potions that might be corrupted by lesser materials. Its use implies value, purity, and magical significance.

Crystals appear in several distinct forms and contexts throughout the magical world, serving both practical and environmental purposes.

The most famous use of crystal is in the form of a Crystal Ball for scrying.

• In Divination classes at Hogwarts, students are taught by Professor Trelawney to “unfog” their Inner Eye and perceive images within a crystal ball.
• The balls are described as perfectly clear glass-like spheres. Professor Trelawney's classroom contains numerous large crystal balls, each resting on a brass or wooden stand.
• Most students, such as Harry Potter and Ron Weasley, have great difficulty seeing anything other than “swirling white fog.” During a third-year exam, Harry sees a shape he believes to be a stag, which Professor Trelawney interprets as the Grim.
• Hermione Granger considered crystal-gazing to be “a very woolly discipline” and ultimately dropped the subject.

High-quality crystal is used to create phials for storing magical substances that require preservation in a pure, uncorrupted state.

• Memories: Albus Dumbledore stored his own and others' memories in meticulously labelled crystal phials before viewing them in the Pensieve. These included his first meeting with a young Tom Riddle and Horace Slughorn's altered memory about Horcruxes.
• Potions: Extremely valuable or powerful potions are often stored in crystal containers. When Harry Potter won a small bottle of Felix Felicis from Professor Slughorn, it was described as being contained in a “tiny glass cork-stoppered bottle” that looked like a crystal phial. Veritaserum, a powerful truth potion, is also kept in such containers.

In the sea cave where Lord Voldemort hid the locket Horcrux, a crystal goblet was present as part of the curse's protection mechanism.

• The goblet rested on the edge of a stone basin containing the potion that concealed Salazar Slytherin's Locket.
• It was the only object capable of scooping the emerald-green potion from the basin.
• After being used, the goblet would magically refill itself from the basin, forcing any prospective thief to drink the entire enchanted liquid to reach the Horcrux.

The term “crystal” is also used to describe magical environments and objects of great beauty or power.

• The Horcrux Cave: The ceiling of the cave containing the locket was described as being studded with crystals, which cast a faint, eerie greenish light over the underground lake.
• Department of Mysteries: In the Time Room, a large crystal bell jar housed a hummingbird that was trapped in a temporal loop, constantly hatching, flying, and reverting to an egg. A “glittering crystal cabinet” in the same room contained the Ministry's entire stock of Time-Turners.
• Yule Ball Decorations: During the Triwizard Tournament, the Great Hall was decorated for the Yule Ball with walls covered in sparkling silver frost and a ceiling of icicles, giving the entire chamber a magical, crystalline appearance.

• In the film adaptation of Harry Potter and the Half-Blood Prince, the cave containing the locket Horcrux is depicted with massive, jagged crystal structures rising from the floor and ceiling, a far more dramatic representation than the book's description of a crystal-studded ceiling. (film)
• The real-world practice of crystal-gazing, also known as scrying, has existed for centuries and is the clear inspiration for its use in Professor Trelawney's Divination class.