Book of Gems from Ruby Play arrived in 2020 and slots directly into the book-slot tradition, swapping Egyptian motifs for a gem-and-adventure aesthetic. The 5×3 grid runs across 10 paylines, with the Book of Gems serving double duty as both wild and scatter — the single symbol that holds the entire mechanic together. Bets start at $0.20 and reach $100, and the high-volatility profile signals clearly that this is a game for players who can tolerate variance in pursuit of the bigger outcomes the bonus delivers.

The gem theme is executed with clean, bright visuals: rubies, emeralds, sapphires, and diamonds fill the upper pay table, while the Book of Gems anchors the screen as a glowing artefact. Wild substitutions in the base game help the 10-payline structure form winning combinations with useful frequency, though high volatility means the base game is often a waiting room for the free spins rather than a consistent pay source in its own right.

Three or more Book of Gems scatters trigger the Free Spins feature. Before the bonus begins, the reels randomly select one gem symbol to act as the special expanding symbol for the entire round. Whenever that chosen gem appears during free games — on any position, any reel — it expands to fill the full height of its reel. Multiple simultaneous appearances of the expanding symbol across different reels can produce full-coverage wins across all 10 lines, and that is where the 5,000x ceiling becomes genuinely reachable.

A Bonus Buy option is available in eligible markets, allowing direct access to the free spins round. The RTP is 96% and volatility is high — the two markers that define the risk-reward shape of the game. Maximum win is 5,000x.

Book of Gems is a well-built, focused entry in the book-slot genre from Ruby Play. The expanding gem mechanic works cleanly, the Bonus Buy adds accessibility for direct play, and the 5,000x target gives the bonus real weight. Recommended for high-variance players comfortable with the format.