Answer:

zirconia

Answer	Crossword Clue
ZIRCONIA	Cubic stone?
ZIRCONIA	Cubic ... (synthetic gemstone)
ZIRCONIA	Compound used in abrasives

ZIRCONIA	Cubic ... (gem)
ZIRCONIA	Metal oxide in dental crowns

Crossword

a puzzle consisting of a grid of squares and blanks into which words crossing vertically and horizontally are written according to clues.