Justin
CA(cyanoacrylate) is one of the ways to go.
There are various viscosity you can use but thin is the most penetrating.
How wide is the crack. Send a pic if you like.
Whats nice about the CA is that you can overfill and then shave down with a razor held firm at 90 degrees.
Bonstone makes a two part express epoxy that comes in a 50ML syringe.
If the crack has some width to it this product could be an option.
You can get creative and use an small assortment of color like stone dust or pigment used lightly to enhance the fill.
Just don't overdo it. The clear glue will pick up the color of the stone if the crack is tight.
It might be prudent to shore up the broken piece as well.