Crystalcore is an aesthetic centered solely around crystals and gemstones of any variety; clear or opaque, colored or monochrome, raw or polished.
Crystalcore visuals focus, obviously, on crystals. It's one of the few aesthetics that, alone, can be very beautiful and magical, but it can only be accentuated by blending with other aesthetics, especially the more colorful aesthetics (given the variety of colors that can crystals can come in) or magical aesthetics (given the association of some crystals with the supernatural) though that's not to say it can't blend with aesthetics that don't fall under those categories. Crystalcore can also be seen very frequently in Icepunk, Seapunk, and Vaporwave in particular, given the ethereal nature of the three (and Icepunk in particular deals with ice, which can take on a crystalline appearance itself).
As for entertainment associated with Crystalcore, one can either watch the JTV channel on YouTube or Steven Universe on Cartoon Network
Crystalcore fashion follows the example of the crystal; bright, colorful, and shiny. Because of this, Crystalcore fashion can borrow very heavily from Raver and Y2K fashions, but also incorporate a lot of jewelry (or rhinestones, if you're on a budget) into the overall look. So if you own any shiny or shimmery pants, shorts, skirts, dresses, shoes, shirts, etc, you can wear a Crystalcore fashion.
A lot of Crystalcore music can have a "glittery" sound like you're walking through an ice cave or into a room covered in shiny jewels.. A lot of Synthwave, Chillwave, Vaporwave, and Seapunk music can evoke this sort of feeling, as well as a lot of New Age music.