Dragon scales sparkled like gems.

Meaning: The dragon's scales were very shiny and beautiful, just like valuable jewels.

Choice of Words: Dragon is a mythical creature often depicted as a large, winged reptile. Scales are the hard, protective plates that cover the body of a reptile. Sparkle means to shine with a bright, intermittent light. Gems are precious stones, often used in jewelry. This sentence compares the scales of the dragon to the brilliance of gems.