I'm using stones and rocks laced with mica. That's what the shiny bits are in some of my works and I usually pick them up in river beds or on walkways, even the side of the road. I can't help it.
Mica is a naturally occurring mineral found in rocks such as granite and schist. It forms in delicate layers that can be peeled into incredibly thin sheets, giving it a distinctive shimmer/sheen. Depending on the light, it can look subtle one moment and luminous the next.
It's one of those materials that turns up in surprising places. Mica gives many cosmetics their pearly glow (yes, you are smashing smashed rocks into your skin), it helps strengthen paints and plastics, and it's even used in electronics because it's such a good insulator. It also has a long history in lighting, thin sheets of mica were used in lamp shades to create a warm glow and soften the light.
Lucky for me, Mica is abundant in parts of Scotland, particularly in the Highlands, where it can often be found sparkling in ancient metamorphic rocks (there is a Mica mine here too). Once you start noticing it, you begin to see flashes of it everywhere. Reflecting light back in unexpected ways and constantly changing as you move around a piece. It's a material with a fascinating geological story, but it also feels a little bit magic.