The moon, for the most part, influences our emotions. In certain phases of the moon, the predictions made through the study of astrological phenomena that would otherwise occur fail to happen, because our emotions do not produce the reactions to the astrological phenomena that would normally be expected. In other phases of the moon, astrological phenomena of planetary alignments and their effect on the Zodiac sun signs are not altered from their original reading.
Envision that astrology is made up of the study of all of the planets and the sun. The astrological birth chart and the study of how planetary alignments affect sun signs are based on these aspects of astrology. The moon actually influences this overall picture, and can cause certain aspects of astrological phenomena to influence our lives differently than was otherwise predicted.
It is not a very expensive stone and is made into necklaces or bigger pieces for jewelry purposes. I especially like the deep, dark blue version with golden pyrite sprinkles creating very unique patterns mined only in Afghanistan. The lighter blue, grayish variety is found in Chile.