Black Onyx and Cubic Zirconia Pendant with chain

Vintage Black Onyx and Cubic Zirconia on Gold Pendant Like new, the shiny teardrop shaped 1/4 in. black onyx gem is highly polished and prong set above a gold frame (Gold is unmarked but tested 10K - so at minimum is gold-filled). There is tiny cubic zirconia at the top that shines like a diamond (too small to tell if it is a diamond). There is a hallmark on the back but I cannot make it out. The whole pendant is 1/2 x 1/4 x 1/4 inches. I have included a 17-1/2 inch gold-tone chain N-291