Geology Question: Mystery Rock!

Hi community! I have a somewhat absurd but real question. My late grandfather-in-law bequeathed us a large rock about the size of a newborn baby. Supposedly it is valuable, but since he has passed away, any specific knowledge he had is not available to us. I went into my friendly local rock store and tried to get information about this rock and they told me to google it. I did not subsequently google "what is up with this large rock" since I figured it wouldn't help. But anyway, I'm kind of out of ideas! How does a person find out the value of a large rock? Do I bring it to a jeweler or something? I wrote to Cal Geology and nobody responded. Any ideas would be much appreciated!!!