How can you tell if a recording is in mono?

I am listening to an SACD pressing of Coltrane's A Love Supreme. I noticed that the stereo imaging was basically non-existent-- Trane is coming from the left channel, drums from the right, with piano and bass in the middle.

Since I have a preamp with a "mono" switch, I used it, and the sax and drums came right into the center along with the rest of the band. However, the sound lost a lot of its sparkle.

Not really sure what's going on here, and would love input.

Hi Dkidknow,
As much as it takes some getting used to,this is the way alot of recordings where made in the early to mid sixties when engineers where fooling around with their relatively new 'stereo' process.Listen to the Look of Love on the famous 'Casino Royal'. Dusty way right with the piano, and percussion to the left.Just strange. I assure you that Love Supreme is recorded that way. Alot of Rudy Van Geller engineered stuff is left/right.I also not surprised that the mono made it lose its sparkle. It is a stereo recording
Montejay is correct, a lot of stereo recordings in this era were mixed with hard panning. Rock music from the early era of stereo is notorious for this stuff, the reason I generally prefer mono recordings from this era.

I suspect some of the sparkle your speaking of is air around images, stereo is often more spacious/airy sounding than mono with it's more tightly bunched images. You also lose a lot playing stereo recordings in mono, artificial mono produces strange effects.
Mono recordings present the same sound from both channels, there is no separation of voices and instruments, it is all unified in the presentation. If you are getting Trane in one channel and drums from the right with piano in the middle, that is stereo. You might have a small soundstage on this recording, but it is definitely a stereo mix.
If you get different sounds in left versus right, you are getting stereo. The sounds you hear in each is a result of the way the stereo recording was mixed and mastered. It is what it is.

When you hit the mono switch, the two channels are merged and the same sound comes out of both speakers resulting in a "mono" image that you gear has assembled from the original stereo.

If the recording is mono and not stereo, you will get similar results to listening to the stereo recording with the mono button/processing engaged even when it is not engaged because the recording itself is mono to start with.

This is all the way it supposed to work, so consider yourself fortunate....there is nothing wrong to be concerned about.
How about disconnecting one speaker and see if you can hear everything coming out of the speaker that is still connected.
Would that work anyone?
If using 2 speakers the sound will be in the center between the speakers, no left or right sounds. The sound stage will be narrow.
Gawdbless, that could probably work, but it would be easier to just use the balance control on your preamp or receiver.
Some old tuners have a built-in scope, or you can use a seperate oscilloscope. When measuring right vs left on a scopes x-y mode, mono will be a diagonal line with no with, while stereo will be a diagonal 'squiggle' (for lack of a better word) varying in width.
Personally I hate mono and the early sixties ping pong stereo inspite of great music of the era - John Coltrane, Miles Davies, Sonny Rollins to name few.

I stay away from any recordings prior to 1959 and early sixties. IOWS, anything recorded before 1959 would be mono ( someone pl, correct me if I am wrong) I am talking about the ones available on CDs. As good a digital system I have (IMO), the re-mastered recordings ( classic jazz) from this era have that high freq tinge around analog notes that it is annoying. (may be the inorganic nature of the recordings has something to do with it) Same recordings played back on LPs are much more bearable though. Not great but bearable. I am referring to Jazz recordings. Classical recordings on the other hand from the early stereo era on Vinyl sounds great.

IMO, recording technique/s have come a long way ( excluding compression mastering taht is on going on commercial releases). May be I am getting way off topic....
Unfortunately, some of the greatest music recorded was in the "Mono" era. I guess one has to weigh whether it is worth it to listen to a great performance even though the sound quality is not up to snuff.
I never used to care for older mono recordings but I am finding many from the 50s in particular to be very enjoyable of late.