geyserite

Geyserite \Gey"ser*ite\ (g[imac]"z[~e]r*[imac]t or
   g[imac]"s[~e]r*[imac]t; 277), n. [From {Geyser}.] (Min.)
   A loose hydrated form of silica, a variety of opal, deposited
   in concretionary cauliflowerlike masses, around some hot
   springs and geysers.
   [1913 Webster]
    

Opal \O"pal\, n. [L. opalus: cf. Gr. ?, Skr. upala a rock,
   stone, precious stone: cf. F. opale.] (Min.)
   A mineral consisting, like quartz, of silica, but inferior to
   quartz in hardness and specific gravity.
   [1913 Webster]

   Note: The {precious opal} presents a peculiar play of colors
         of delicate tints, and is highly esteemed as a gem. One
         kind, with a varied play of color in a reddish ground,
         is called the {harlequin opal}. The {fire opal} has
         colors like the red and yellow of flame. {Common opal}
         has a milky appearance. {Menilite} is a brown impure
         variety, occurring in concretions at Menilmontant, near
         Paris. Other varieties are {cacholong}, {girasol},
         {hyalite}, and {geyserite}.
         [1913 Webster]