Solar gem

A very rare type of gem that is somehow connected to energy from the sun. The gem changes color based on the position of the sun. At the darkest part of night the gem is obsidian black and as the sun start to rise the gem gradually becomes brighter until dawn where it becomes colorless transparent. As the sun rises it starts to take on a yellowish color until the sun reaches its highest point and the gem becomes bright gold in color. As the sun sets the crystal again moves toward transparent, and finally black.

The gem is a valuable tool for navigations as it allows the owner to know when it is noon and thereby getting an accurate longitude. Because of its scarcity and very high cost very few ships has a gem. Many naval forces equip the lead ship with a crystal and let the ship guide the armada.

Some mages has found use of the crystals in various spells and tools and the crystals are sometimes used simply as decoration where the high price make them a status symbol.