It broke just below the cameo, and it wasn't a clean break, but several chips and tiny splinters of glass in the packaging. It does have a mould line down the stem. I would love to know what it is. The opalescent glass fluoresces under UV light, and has a lovely shine, more opal like than any similar glass I have seen before, almost red in the light.
It wasn't really very well packed, with just one layer of bubble wrap around it, and then the space around it in the box filled with crumpled newspaper. I bought two items together, the other was a bowl with a metal rim, and he had stood the stem in the bowl, but not packed it around, so it looks as though it has banged against the metal rim, which would act like a hammer I should have thought.
I am still waiting to hear back from the seller.
Here are some more pictures to help with identification.