What one might lack in the way of photo technique and equipment to tackle those "don't show-up well" things, there is always the utility of perfect descriptions, as I believe you managed quite well with "shiny dust that's hard to photograph". There are two very common inclusions that present as both shiny and elusive to film: Pyrite (and its relatives) and Muscovite mica. Mica is present under high temperatures and pressures and therefore represents a product of some amount of mineral metamorphism. It occurs in quantity when a sedimentary rock like shale is moderately well staged through metamorphism to become a rock called schist. The lower sections of the Georgian Bay shoreline have a history of sedimentary deposits: sandstone, limestone and shale. Areas where the Canadian shield meets the sedimentary plane of southern Ontario is where schist appears, such as Hastings County (Bancroft).
Muscovite mica in large plate-form
Shale that has been moderately changed by temperature & pressure to
phyllite
A sample of schist, aka mica schist, aka Chlorite schist. Small quantities appear like specs that glitter, or even dust if very fine. When larger crystals develop you get the actual rock form of schist. Chlorite schist is just another form of schist. If it is composed of Muscovite mica it will be brownish (at least in Ontario), if it contains black Biotite mica then it is black, if it is rich in chromium it is bright green and is called Fuschite, if it contains lithium it is lilac-coloured and is called Lepidolite. All of these mica forms can be present as flaky stone with a cleavage along plates and form the rock schist, or just be present in both igneous rocks (granite) or metamorphic rock (gneiss).
Biotite mica
Lepidolite mica
Larger crystal version of Lepidolite
