What's the deal with Microgrove LPs?

I recently raided my girlfriend's elderly aunt's record collection and came away with a few 7" records labeled: "CBS Masterworks." They're from the 1950's and say they are
"microgrove" LP's, but nowhere does it say at what speed they play.
I can't tell if they're 45 or 33 1/3 or something else.
Has anyone heard of these and is there any issue with respect to today's needles?
The grooves do look very close together.
7" of 50's are always 45rpm and there's no issue with current sound pickups. I'd be cautious about condition of these not to damage your speakers with loud clicks pops that may occur.
These sound like 78's to me ..are they real thick?
I have 7" and 10" LPs and they are 33rpm. Yours are CBS/Columbia and are likely to be, as well. 45rpm was RCA's thing.
Is that "Microgroove" or really single 'O' "Microgrove"?
Miicrogroove was the buzz word as opposed to the 'old' style 78's.
So "Microgroove only means they are NOT 78's.
They may play at 45 or 33. (IMO most likely at 33)
They may have been freebies given away with some other music...
Microgroove is a term from the 50s.The first records after the 78 were 10" to fit the shelving which already existed for the 78.The 78 has a wider groove.The new groove was narrower therefore called microgroove.This is the same size groove used today,so play on.On some 50s-60s turntables you had a flipover cartridge with a 78 stylus on one side and a LP (microgroove) stylus on the other side.
Thanks, but there seems to be some disagreement as to whether they'll play at 33 or 45. Not a real big deal, I'll figure that out easy enough. As long as there are no issues with today's cartridges, but as Czarivey admonishes: I'll be careful.
To Mattmiller: Yes, they are pretty thick.
To Ghosthouse: You are correct, it should be a single "O" not Groovy!!
To Elizabeth: I think you are also correct. They may have been freebies b/c old authie did belong to a record club as some of her LPs state they're from the club.