| Answer | Crossword Clue |
|---|---|
| MICA | Sparkly rock substance |
| GNEISS | Sparkly rock |
| GEODE | Sparkly rock |
| substrata | An underlying layer or substance, in particular, a layer of rock or soil beneath the surface of the ground |
| porosity | the ratio, expressed as a percentage, of the volume of the pores or interstices of a substance, as a rock or rock stratum, to the total volume of the mass |
