What is modern fire alarm cable made of?
That sounds like FP200 or similar. 

The copper tube with mineral insulation was MICC cable.

MICC is a pain in the arse to terminate which is why no installer likes doing it if they have any choice, and the modern synthetics have good enough properties in a fire to make them compliant with the appropriate standards and are not hydroscopic if incorrectly terminated. 

MICC tended to fail insulation test after a while if the person fitting the potting gland on the end was not taking sufficient care.

There are multiple vendors of modern fire alarm cables and they all have their own trademarks and 'secret sauce' chemistry.