Thanks for the ID. After looking at other images, I'm sure that's it. Ross, if I remember, it was about 1/2" in length, not including the ovipositor.

I can't find a "common name" for this wasp anywhere. Is there one?

When are common names needed? Probably never, but least of all for things that are rarely seen and little known, such as Acanthochalcis nigricans. No hosts or plant associations appear to be known for this species, and, as far as I know, the Nevada records here on BG may be the first for that state, as Nevada was not among the states recorded in the 1979 catalog of Hymenoptera.

When I have "Bug Books" printed for my grandkids, or have a photo album of my own macro-photography at the house that laypersons might look at, it seems much more appropriate (and interesting) to have the pictures labled with common names rather than scientific/latin. Such names sometimes hint at information about the creature or lead to questions and discussion. Nursery Web Spider, Blue-steel Cricket Hunter, and Antlion Lacewing seem infinitely more interesting in these circumstances.
By the way, these wasps are parasitoids of beetles, particularly Buprestidae, on the following plant hosts: Saltbrush, various Brooms, Oaks, and Ocotillo.

I see now that Halstead published on the biology of the species back in 1985. John Noyes evidently did not catalog that information in his Universal Chalcidoidea Database. The scientiic name of the organism has its descriptive qualities, meaning, I presume, the blackish spined chalcis. I suppose spine (acantho) may pertain to the ovipositor being longer relative to body length than is typical among Chalcididae.

Yes, of course I agree that scientific names usually have decriptive qualities, and when everyone in my family and all my friends learn Latin, I shall quit using common names :D