The phrase "are of two varieties" is correct and usable in written English.
It can be used when describing items, concepts, or categories that can be classified into two distinct types or forms.
Example: "The fruits in the basket are of two varieties: apples and oranges."
Alternatives: "come in two types" or "exist in two forms".
The microfossils occur in cherts and shales and are of two varieties.
The bonds are of two varieties: general obligation, where debt is secured by the state's ability to tax, and revenue bonds, where principal and interest are paid by a designated revenue stream.
It seems to me that the people who buy semi-automatics and military gear for hunting are of two varieties -- those who 'pretend' they are hunting and killing men; and those living out fantasies of resisting a tyrannical government take-over.
Approaches for mass spectrometry (MS -based MS -basedics can be of two varieties: targeted and discovery.
The poetry was of three varieties: religious, love and nature.
The pink and flaky salmon sitting on your dinner plate can be of three varieties: wild, farmed or hatched.
The eight sources of barley were selected from 32 sources; the eight sources were of six varieties, two growing years, and six growing locations and were representative of the range in chemical composition and bulk density found in the original 32 sources.
The Pd II) components used are generally of two varieties: cis-protected Pd II) and unprotected Pd II).
These waves of motion can be one of two varieties: primary ("P waves") or secondary ("S waves"), which move at different speeds.
Renaissance chairs were of two principal varieties: those light enough to be moved easily and those heavy thronelike seats used by the head of a household or other important people.
They are one of four varieties that D'Artagnan has just introduced.
