Here’s another sample provided by Reiner Mielke from the Dundas quarry; it is a mineral called Sphalerite. Sphalerite is a native form of zinc sulfide and, according to my research, can be ‘white’, to ‘honey-yellow’, to ‘brown or reddish’. My own powdered form is light brown in colour but I have yet to see if heat will change that. It also seems to have very good hiding properties as it covers well.
In reading a bit about this mineral, I was surprised to learn that in this natural form sphalerite has a pigment name! It has historically been called ‘Blende’.