anrākerel

anraakerel

anrākerel

made of or from opal (Hydrated silica. SiO2·nH2O).

Names of substances, including minerals, are generally given in the stative, as they are considered to be attributes. A piece of opal would be referred to with the singular jarākerel.

pa jakīþa anrākerel;
The rock contains opal.

More literally, the rock has an attribute: opal.

la jakīþa jarākerel;
The rock is opal. (or, The opal rock is.)

A picture (by me, taken in Australia):

P9200016