It is certainly possible to make convincing imitations of Méxican green-stone beads—because they tend to be crude constructions. But here are two points to remember:
1) The authentic beads have been fairly common and available over the fifty years I have collected and studied beads. No doubt with periods of fewer or more beads appearing at one time or another.
2) The Guerrero industry that makes "reproductions" of pre-Columbian beads has largely made beads that are "too nice" and refined to appear authentic. The material is more-colorful than are many old beads, the shapes are more even, and the drilling is straight and not biconical. Plus the material is more likely to be serpentine than granitic.
One exception I can think of was when I bought two strands of "pre-Columbian crystal" beads that looked quite authentic. When I got them home, I looked at them more carefully—and was surprised to find they were actually made from glass. (Lapidary-worked and drilled.) But, these were not green-stone beads. After I returned them, I was sorry—because I'd like to have them in my Fakes Collection.
I would also make a judgement based upon what I can see. Whether there are expected signs of great age; and what the material and details look like. One cannot be 100% right all the time. AND, it can be difficult to be too confident from a photo. Which is why I said your beads "look OK," rather than that I am sure they are authentic. JDA.
thanks! I'm learning a lot here in this forum. Do you know anything about how these beads make their way onto the modern market?
Just as these things often happen.
People in the bead business who love México, travel to México, buy beads, return, and add them to their inventories. I have two friends who so-participate. One is the friend from whom I bought the glass imitations I mentioned, from whom I have also, at around that time, bought green-stone beads and modern stone beads from Guerrero. JDA.
Thank you! I wanted it more symmetrical so went back the next weekend to get a few more -- here is the final necklace.