He is an expert in gemology, and he is good at evaluating the quality of diamonds.

He is known as an expert in gerontology.

Semiotics is the study of signs and symbols used in society and culture.

He is an expert in crystallography.

He is majoring in humanities at university.

I am majoring in parasitology at university.

He is majoring in metallurgy at university.

He is reading a book about demonology.

He is an expert in enzymology and conducts many researches.

He is an expert in oenology and has a deep knowledge of wines from around the world.