Can carrying rose quartz attract someone you like?
Slate will not stand up to heat as well as quartz will. Hardly surprising considering quartz began as a form of lava, while slate began ad a sedimentary rock. So regardless of its reflective properties, slate would be inappropriate to use.
Why are you asking this in anthropology? Anthropologists don't spend there time dealing with the physical properties of rocks, unless they were used in some way by hominins.
I would say slate would reflect heat back at you better than quartz, also, slate when heated, should retain the heat longer than quartz.
FYI-- all rocks start out as igneous rocks, and over time, erosion creates sedimentary rocks. Quartz hasn't undergone the kind of heat, pressure, or weathering that slate has undergone. Slate is better for heat, though.
