I was told the rod I bought from another member was ND:YAG, but the man it was purchased from earlier said it was glass, I didn't think so. Thanks guys.
Yeah, I somehow lost sight of the original questions when I went off on a tangent about Nd:GLASS rods. My mistake. Should have stuck to the original question.
Take a pair of calipers, measure carefully the rod length and diameter in centimeters. Weigh it on an accurate gram scale. Weight divided by volume = density.
YAG has a density of ~4.6
Phosphate type 750 laser glass has a density of about 2.4 , others have a density around 2.9 or so..
Schott's Numbers near the bottom of this link. Hoya Glass will be similar