hydrophane

hy·dro·phane

 (hī′drə-fān′)
n.
An opal that is almost opaque when dry but transparent when wet.

hy·droph′a·nous (hī-drŏf′ə-nəs) adj.

hydrophane

(ˈhaɪdrəʊˌfeɪn)
n
(Minerals) a white partially opaque variety of opal that becomes translucent in water
hydrophanous adj

hy•dro•phane

(ˈhaɪ drəˌfeɪn)

n.
a partly translucent variety of opal that becomes more translucent or transparent when immersed in water.
[1775–85]
hy•droph•a•nous (haɪˈdrɒf ə nəs) adj.
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References in periodicals archive ?
Both specimens increased in weight after hydrostatic SG weighing, and after one week they still retained a slightly higher weight, indicating some degree of hydrophane character.
When these are heated, the wonderful array of colours disappears because the water has been driven off and there are some opals, such as hydrophane, that only show colours when in water.
broke slowly through the skin like eyes from closed lids, and became opal--fire opal, black opal, gey-serite and hydrophane, full of watery light.