A fragment of the Moon
Moonstone is also known as the birthstone of the Cancer Zodiac.
Due to the Cancer Zodiac being connected to the moon throughout the ages being referred to as Lord of the Moon, the stone with it's light-bending properties is also often connected to the constellation.
It's light bending properties were so radiant in some cases that ancient cultures believed that it would stimulate what is known as the pineal gland, a part of our brain which is also known as the seat of the soul. Due to this, it was valued for being able to attune and center you.