Hello, I used to (and still do to some extent) sell a fair amount of turquoise. Look at the dark matrix (host stone) with a jeweler's loupe. A dark brown to black matrix is typically iron based and iron pyrite, and sometimes you can see some glitter of pyrite, or larger shiny areas. So far as I know iron will not be affected by a hot needle, and should not dent or burn (of course unless in a blast furnace). A turquoise bead with a lot of dark iron matrix should be heavier than a plain turquoise bead I would think. You also want to see a certain organic "fuzzy" interplay between the black matrix (even polished can have a surface irregularity and tiny pitting-though this could be filled in with surface wax) and the turquoise- visible with a loupe if you look along where the colors meet. Can you take some close ups of the beads with the dark veining?
While the color variation in the bead in the bottom right 2nd photo is reassuring, the hot pin results don't make sense.
Anne