Today we'll begin with a test. Look at the picture below, and tell me... is it a xylophone? Or a glockenspiel? Or something else?
This was actually an unfair test, because I deliberately chose a picture of a child's toy, and everyone knows that those things are xylophones -- they say so right on the package!
Or are they?
The truth is, despite the fact that the toy's packaging probably said, "Toy Xylophone," this is not a xylophone at all (though it is a toy).
This is a glockenspiel.
So what is the difference? The difference is in the material used to make the bars. If the bars are made of metal, the instrument is a glockenspiel. If they are made of wood, it is a xylophone.
Consequently, xylophones have a much more mellow sound than glockenspiels (imagine striking a mallet against a piece of wood, and then striking a mallet against a piece of metal!).
And where does the marimba fit into all of this?
A marimba is like a xylophone, except that it has resonating tubes under the wooden bars, which amplify the sound. Marimbas tend to be lower pitched instruments than xylophones.
While all of this might be interesting, none of it helps us remember whether a xylophone is metal or wood.
It would be obvious, if only we had been taught the Greek-origin prefix "xylo," which simply means "pertaining to wood." It would also be obvious if we knew that a coconut is a xylocarp because it has a "woody" shell. Or if we knew that xylotomy is the microscopic study of wood. Or if we knew that xyloid is a synonym for "woody." Or if we remembered from biology class that xylem is one of the types of transport tissue in vascular plants (such as trees). Unfortunately, none of these "xylo" words are well known.
So maybe this will help: A glockenspiel is the only kind of glock you should ever give a child.