JMT "sparkle" effect?

[Alpenbro]

Last year my wife and I took a trip to Cathedral Lakes/Sunrise HSC in mid September. On the hike out back to the meadows it was a sunny day and we noticed little "sparkles" in the trail. It literally seemed like the trail was twinkling.

Finally it dawned on us that this part of the JMT, being heavily used and a little sandy had formed tiny bits of glass in the trail from all the grinding boots and hooves over the years which would catch the sunlight and yield this "sparkle" effect in the right conditions. It was magical and something I'd never seen before.

Have other hikers noticed this too? Which trails? It was really cool and something I've been wondering about ever since..

[The Other Tom]

Interesting. I've never seen this before. I guess you have to catch the light just right. Maybe someone who has more geologic experience than I do can chime in, but my guess is that it was quartz crystals that were reflecting the light.

[giantbrookie]

Many of the trails of the Sierra have sections where the trail bed is essentially granitic sand. The granitic rocks are generally composed of quartz, feldspars, and micas. The sparkles most likely come from cleavage faces of the feldspars and the micas.