The shape of gold crystals inside sapphire has been studied by transmission electron microscopy. 400 keV gold ions were implanted into sapphire (α-Al2O3) at a substrate temperature of 1200°C. The gold ions precipitate as small crystals, which have an ordinary f.c.c. structure and dimensions less than 60 nm. The small gold crystals clearly have faceted outlines. The sides of the outlines are parallel to low-index crystal-planes of sapphire. It has therefore been concluded that the shape of the gold crystals is characterized by the foreign crystal (i.e., sapphire), and that the shape should be a tetradecahedron which consists of two {0001} and twelveplanes of sapphire.