Unknown mite species in plant pots
These look a lot like dust mites, a collective term to describe cosmopolitan house-dwelling mites in the Pyroglyphidae family.

The most common species in temperate regions belong to the Dermatophagoides genus, including D. pteronyssinus (the European house dust mite) and D. farinae (the American house dust mite).


 source: Wikipedia 

See here for a closeup of D. pteronyssinus

Alternatively, they may be &quot;storage mites&quot; belonging to the Acaridae family, which are another group of common dwelling-inhabiting mites that are more often found in stored foods vs dust, upholstery, or carpeting.

Lepidoglyphus destructor is one such example but that is also found to be present in dust [Source: Juliá et al.(1995)]. Another common storage mite, Tyrophagus putrescentiae typically eats mold, and could be found outside a food setting if the mold density was prevalent enough.


 L destructor (according to M. Deml on biolib.cz) 

I'll note that there are hundreds of mites in these two families of mites alone, so someone may be able to get to a more specific species for you. Knowing more about where you found them (species of plants, etc.) may or may not help narrow down more specifically. For example, the person in this forum post found a very similar looking mite on their pots as well (see here). 

Description:

Both male and female adult house dust mites are globular in shape, creamy white and have a striated cuticle. The female measures approximately 420 microns in length and 320 microns in width. The male is approximately 420 microns long and 245 microns wide.  [Source: UFL.edu]

Human impact:
The genus name Dermatophagoides means &quot;skin eater,&quot; but these mites are not parasitic. Their diet mainly consists of eating dead skin flakes from mammals (and some birds).  Human detritus is one of the primary food sources for these mites, and so it's no surprise that they are often associated with dust in human dwellings.
So these mites don't bite humans or burrow into their skin. However, they do tend to have a negative impact on humans. Specifically their digestive enzymes remain in their feces, and these dried fecal enzymes (along with their dried dead exoskeletons) cause allergic reactions in people. In fact, according to Raulf et al. (2015), 20 allergens are known from just the two species of hdust mites mentioned above!
From UF IAFS

Mite allergens are mainly present in feces of house dust mites and may become airborne and inhaled by patients, giving rise to asthma, rhinitis, or atopic dermatitis


In fact, the family name, Pyroglyphidae, which literally means &quot;fire + carve&quot;, seems to be related to the &quot;burning itchy&quot; eczema that some people develop that results in lots of scratching (carving :p).

Multiple sources suggest that storage mites often have similar allergic impacts as dust mites. Fro example, this site suggests:

In Europe, Lepidoglyphus destructor has been reported to be a major source of mite allergy in rural and urban environments

The question is, how many people are impacted?

Well, according to studies cited again by Raulf et al. (2015) that examined 7000 Germans found that  ~16% had a sensitization to D. pteronyssinus. Other studies (discussed in Hossny et al. (2014)) seem to suggest much higher prevalence in certain populations -- with sensitivities found in up to 90% of people tested from certain populations.

What can you do??
According to UF IFAS:

To manage mite populations, reduce the humidity below 70% and thoroughly vacuum mattresses, carpets, sofas, and chairs. Very sensitive individuals should encase their mattresses in plastic. Use drapes that can be washed and change bed clothing frequently. Vacuuming does not always remove all the live mites and Korsgaard (1982) stresses reducing humidity over sanitation. No one method has been found for reducing mites and relieving allergy suffering. Immunotherapy, i.e., injections of mite extracts into the patients to increase antibody level, has had variable success (Munro-Ashman et al. 1976).

Final word(s):

I'll just mention that there is a ton of literature about these mites and their impacts on humans, so if you're interested, DIG IN!

The [Major Mite Taxa] key by D. E.  walter (find at idtools.org](http://idtools.org/) is an excellent online resource for digging into mite identification further!



Citations:
Hossny, E., El-Sayed, S. and Abdul-Rahman, N., 2014. Sensitivity to five types of house dust mite in a group of allergic Egyptian children. Pediatric allergy, immunology, and pulmonology, 27(3), pp.133-137.
Julia, J.C., Martorell, A., Ventas, P., Cerda, J.C., Torro, I., Carreira, J., Guinot, E., Sanz, J. and Alvarez, V., 1995. Lepidoglyphus destructor acarus in the urban house environment. Journal of investigational allergology &amp; clinical immunology, 5(6), pp.318-321.
 Raulf, M., Bergmann, K.C., Kull, S., Sander, I., Hilger, C., Brüning, T., Jappe, U., Müsken, H., Sperl, A., Vrtala, S. and Zahradnik, E., 2015. Mites and other indoor allergens—from exposure to sensitization and treatment. Allergo journal international, 24(3), pp.68-80.