Some hot , massive , population-I Wolf-Rayet ( WR ) stars of the carbon subclass are known to be prolific dust-producers .
How dust can form in such a hostile environment remains a mystery .
Here we report the discovery of a relatively cool , extended , multi-arc dust envelope around the star WR112 , most likely formed by wind-wind collision in a long-period binary system .
We derive the binary orbital parameters , the dust temperature and the dust mass distributions in the envelope .
We find that amorphous carbon is a main constituent of the dust , in agreement with earlier estimates and theoretical predictions .
However , the characteristic size of the dust grains is estimated to be \sim 1 \mu m , significantly larger than theoretical limits .
The dust production rate is 6.1 \times 10 ^ { -7 } M _ { \odot } { yr ^ { -1 } } and the total detectable dust mass is found to be about 2.8 \times 10 ^ { -5 } M _ { \odot } ( for d = 4.15 kpc ) .
We also show that , despite the hostile environment , at least \sim 20 % of the initially-formed dust may reach the interstellar medium .