IPA: /ɪnˈsɒljʊb(ə)lnəs/
KK: /ɪnˈsɑl.jə.bəl.nəs/
The quality or state of being unable to be dissolved in a liquid.
The insolubleness of certain minerals makes them difficult to process in water.
Insolubleness → It is formed from "in-" (meaning not) and "solubilis" (from Latin, meaning able to be dissolved) and the suffix "-ness" (meaning the state of being). The word refers to the state of being not able to be dissolved.
Think of 'not' ('in-') being able to be 'dissolved' ('solubilis') — that's why insolubleness means the state of being unable to dissolve.