Adrian's phenotype design is inspired by a claystone very common in my area!

The weathering processes alter the outer portion of the stone and give it an off-white colour, while the inner core remains green-grey. The fresh green surface can be exposed by breaking the claystone apart or just chiseling a piece out (which is why Adrian's tattoos are green, it's the exposed fresh surface of their carapace:) (spy their Eridanus constellation tatoo, the star theme to their markings comes from my headcanon that Adrian is an astrophysicist hehe)

The red specks on their design are iron oxide impurities, often also visible on fresh surfaces, bleeding into them and giving them the rusty coloration. And, of course, honorary mention to quartz veins! Those often form when a crack in the rock is permeated by hot hydrothermal fluids which then deposit the quartz in a vein-like structure:)

(Some claystones I hoarded over the years v )

Rocky's carapace is inspired by a sandstone (specifically quartz arenite, which is just a mature variety of sandstone made up mostly of small quartz particles.)

Now, I gotta add some cross-bedding features to my boy: the lines visible on his shell are a common sedimentary feature that often forms in dunes and deserts - the wind carries sand particles in a particular pattern, forming these cascading lines of strata. (These can be used to look back on ancient climates and determine the predominant wind direction in the area btw!)

And finally, for the green inclusions on Rocky, those are also quartz veins, but this time, with chlorite inclusions, to give them the green tinge:)