The phrase "although only rarely" is correct and usable in written English.
It can be used to indicate that something happens infrequently or not often, typically in a contrastive context.
Example: "The phenomenon occurs, although only rarely, in certain environmental conditions."
Alternatives: "albeit infrequently" or "though seldom".
Conspiracism is an American tradition, Professor Goldberg writes, although only rarely, as in the 1850's and 1930's, do the conspirators seem even temporarily to have penetrated vital institutions.
He will also build a number of simple nests (cock's nests) to show to his mate, although only rarely will she complete the structure, usually starting afresh.
Although only rarely, we found some cases in which our algorithm did not work as expected.
C. elegans has been found in most parts of the world [ 4], although only rarely in the tropics [ 5].
The ex-smoking prevalence was generally increasing over the time periods investigated in both sexes and all age groups and was lower in American-blend than Virginia-type markets, although only rarely with statistical significance.
This species occurs from sea level to the highest peaks, although it only rarely occurs at lower elevations.
Thus, MgO (periclase), although occurs only rarely as an oxide, we choose it here for our study.
Those near the top of the list get Commons debating time, although they only rarely make it to law.
Although previously reported only rarely, we conclude that MASC may show expression of basal/myoepithelial markers.
Although the entries only rarely list a diagnosis, it is clear that most of the patients Geddings saw were suffering from pulmonary diseases or tuberculosis.
Campaign season brings a spike in the killing, although homicides are only rarely solved here and political crime is no exception.
