The earring itself is hemispherical and is encrusted with the
hematite which provides the "twinkle" shine. The settings are
fairly robust. How sensitive is hematite to heat?
I’m no authority, but in my experience, hematite is not at all
sensitive to heat. I found out the hard way that it retains heat for
a surprisingly long tine… Maybe not surprising, since it is mostly
iron (Fe2O3, according to Wikipedia). But my fingers were still, um,
However, chances seem good to me that what you have is not hematite
but marcasite (FeS2) which is commonly used the way you describe.
Never seen a faceted hematite (not that that proves a lot).
I cannot tell you whether marcasite is sensitive to heat.