@Baley
Proper identification of mites is a very difficult task. The identification requires mounted adult specimen (cleared and prepared on a slide), usually a series. The identification of mite larvae (nymphs) is often impossible. You need the prepared slides to see microscopic details, such as hairs, mouthparts and genitalia, which are important for identification.
You can make an educated guess based on ecology and macroscopic images, as with
Balaustium here, but a "save" determination requires more effort.
Here is a primer on mite preparation:
http://www.publish.csiro.au/web_cds_dem ... sification