Can someone explain "Moving Iron" vs."Moving Coil"

I recently got back into Vinyl, and I bought a Sota Sapphire, with an Alphason arm and a Grado cartridge. I asked the previous owner if it was a moving magnet or moving coil cartridge - he told me it was a moving iron. I've got a Classe DR6 preamp - do I select MM or MC on the back of the pre ? I started off with MM and I don't seem to getting sufficient gain, I don't want to switch to MC, as I'm afraid the output of the Grado might be way too high for the MC phono stage. Am I being paranoid, or should I just go ahead and flip the switch to MC and ride the results? Thanks.
Basically, an audio signal is generated by moving a magnet near a stationary coil of wire ("Moving Magnet") or by moving a coil of wire near a stationary magnet ("Moving Coil").
The MM has more inertia which is why MC is generally considered to have a finer sound (can start-and-stop quicker). The MM generates a stronger signal (greater amplitude) and doesn't need such a strong head-amp.
Hope this helps...

Seems I'm off-base with this explanation.
See earlier post "MC or MM".
Ghostrider45 has a good explanation...
To give you a quick and non-technical answer, here are the descriptions of how a moving magnet, moving coil, and moving iron cartridge operate and differ from each other:

Moving coil: the inner end of the stylus cantilever is wrapped with coils of wire (more coils = more signal voltage), and this coil-wrapped cantilever end moves within the magnetic field of a fixed set of magnets. Generally speaking, moving coils have faster transient response than MM's, since there is less mass involved, but the output signal is normally lower than a MM.

Moving magnet: the inner end of the stylus cantilever has small magnets attached to it, and this magnet assembly moves within the coil assembly.

Moving iron: Grado makes so-called moving iron cartridge designs, and here is the explanation of the design that they present on their web site:

This design feature is basically quite simple. The "OTL" cantilever shaft is brought to a fixed axial pivot that supports the entire cantilever assembly. A miniature element attached to the end of the cantilever (the "iron") is allowed to move freely within the lines of flux of a stationary magnet and coil structure. This system of support is mechanically more accurate (more linear) than conventional "teeter-totter" designs that utilize an iron armature to balance the mass of the cantilever. The teeter-totter design is supported in the center with a rubber donut mounting.

The fixed axial design has a very low tip mass, which results in lower distortion, improved transient response, and longer record life. This proprietary design allows the implementation of the Flux-Bridger Generator System.

The Flux-Bridger design uses four separate magnetic gaps that the miniature element of the cantilever (the "iron") bridges. The miniature element moves between opposing flux gaps creating an increase in flux in one gap while reducing it in the other. The four separate magnetic gaps create a highly efficient and perfectly balanced system. This design requires fewer coil turns than conventional designs.

The Grado web site has a good diagram of the internal structure of their moving iron cartridge. Here's the link:
When you get the home page, there are three tabs in upper left corner -- click on "Cartridges".
What Sdcampbell said.
As far as harming your equipment, compare the specified output of your MI cartridge to that of an MC.
If not radically different, turn the volume all the way down, plug into the MC channel and give it a shot.
Call Grado if you want ot be sure.
Most Grado's are not very "hot" in terms of output. They are measurably higher in output than most MC's but lower than many MM's. If you use the MC input, you will probably end up over-driving the preamp, causing noticeable distortion. This would become more apparent on records that are higher in output or during high amplitude peaks.

Out of curiosity, do you know what model Grado you have and what the gain of the phono stage on your DR6 is rated at? Sean
The Grado wood body cartridges are available in both high and low outputs (4.5 & .5 I think). Grado's phono pre which I assume was designed to match these cartridges has a choice of either 45 or 62db of gain. Your cartridge could be a low output model. Try both settings on your preamp and go with the one that sounds best.
Good info Bld. I didn't know that they offered two different output levels for their cartridges. 4.5 mv would be plenty for most any MM phono stage. The .5 versions could be used with MC inputs, but one might want to check the loading. Some MC stages use different loading characteristics than their MM counterparts.

For some reason, i was thinking that Grado's weren't as low as .5 but not as high as 4.5 mv output. Dropping somewhere in the middle there would put someone in a bind in terms of having "almost" enough gain on the MM stage while having too much output for an MC stage. Sean
Should have done some research before my previous post. The current models have outputs of 5mv & .5mv, the gain on the phono amp is 40 or 56 db.
Dbamac: Don't forget to let us know how things turn out?