This page narrows Gem down to Mastery only, so the table stays scoped to one subtype instead of the full category list.
Pricing here moves the same way the rest of the catalog does — Retail pulls hourly from the Blizzard Auction House API, while the classic editions pull from TradeSkillMaster on their own cadences. Each snapshot is timestamped, so the detail page for any row below plots real movement over time.
Use the search box on the item database home page to jump to a specific item by name, or use the breadcrumb above to step back up to the full Gem category.