A gemologist is trained in identifying, sorting, and grading gemstones, while an astrologer interprets celestial bodies to predict human affairs. Astrogemology combines both, suggesting that specific gemstones correspond to astrological signs, planets, and houses, potentially offering benefits related to health, wealth, and relationships, according to some astrologers and gemologists. 

Gemologist: A gemologist's expertise lies in the scientific evaluation of gemstones, focusing on factors like color, cut, clarity, and carat weight to assess their quality and value. They are not typically involved in the astrological aspects of gemstone selection. 
Astrologer: Astrologers study the positions and movements of celestial bodies to interpret their influence on human life and predict future events. This includes suggesting specific gemstones based on astrological charts. 
Astrogemology: This field combines gemology and astrology, proposing that certain gemstones are associated with specific planetary influences and astrological signs. For example, a blue sapphire may be recommended for Saturn, while an emerald might be linked to Mercury. 
Gemstones in Astrology: Some believe that gemstones can help balance negative planetary influences, enhance positive aspects, and attract good fortune. 

Gemstones and their supposed effects:
Different gemstones are associated with various qualities and energies. For instance, a ruby is believed to be beneficial for the Sun, a pearl for the Moon, and a red coral for Mars, according to some sourcess.