He is an expert in rhetoric, teaching the techniques of speech.

He is globally recognized as an expert in Indology.

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.