havikaili = coal (noun) (some things Google found for "havikaili": an unique term; this is a compound Miresua word of havi (stone) and kaili (carbon; coal))
Word derivation for "coal" :
Basque = harrikatz (harri = stone + ikatz = coal,charcoal)
Finnish = kivihiili (kivi = stone + hiili = carbon,coal)
Miresua = havikaili
To be precise, this is the Miresua word for bitumous coal, as opposed to anthracite coal.
Why the conlang words for coal? For one, because this conlang is used in a world that is not modern. Also because I personally know what it's like to burn coal to stay warm. I spend some time, particularly in the warmer months, at an old family house in the mountains that lacks central heating.