From The Collaborative International Dictionary of English v.0.48 [gcide]:
Amianthus \Am`i*an"thus\, n. [L. amiantus, Gr. ? ? (lit.,
unsoiled stone) a greenish stone, like asbestus; 'a priv. + ?
to stain, to defile; so called from its incombustibility.]
(Min.)
Earth flax, or mountain flax; a soft silky variety of
asbestus.
[1913 Webster]