Minutia is a singular noun meaning a small detail. Minutiae is the Latin plural of minutia, and we usually use it in English. Latin plurals are often tricky, and many eventually drop out of English in favor of -s plurals, but minutiae is deeply entrenched and is likely to stick around, at least in more formal and technical writing registers. Minutias does not regularly appear.
But minutia is often treated as a mass noun (e.g., all the minutia is slowing us down), and it’s sometimes treated as plural, as in the first three examples below. If either of these usages becomes more common, we could soon see minutiae begin to fade from popular usage.
Because we usually speak of trivial details as plural rather than singular, minutia should properly be less common than minutiae. But minutia is often used in place of its plural—for example:
We’re hoping that someone is sharing the minutia of our day, even if it is across a broadband connection. [Time]
If you’re like me, you don’t have the patience to wade through all minutia of a sports labor mess. [Los Angeles Times]
They are at their happiest dissecting the minutia found between the lines in polls. [Toronto Sun]
And these writers use minutia and minutiae in the traditional ways:
In an era in which political reporting has become more and more focused on minutiae, he kept his focus where it belonged. [Washington Post]
Every regal minutia was faithfully recorded. [Guardian]
He is also described as a devourer of knowledge, theory and minutiae. [New Zealand Herald]