SINTER  , a word taken from the

German (allied to Eng . " cinder ") and applied to certain mineral deposits, more or less porous or vesicular in texture . At least two kinds of sinter are recognized—one siliceous, the other calcareous . Siliceous sinter is a deposit of opaline or amorphous silica from hot springs and geysers, occurring as an incrustation around the springs, and sometimes forming conical mounds or terraces . The pink and white sinter-terraces of New Zealand were destroyed by the eruption of Mount Tarawera in 1886 . Mr W . H . Weed on studying the deposition of sinter in the Yellowstone National Park found that the colloidal silica was largely due to the action of algae and other forms of vegetation in the thermal waters (gth Ann . Rep . U.S . Geol . Surv., 1889, p .

613) . Siliceous sinter is known to mineralogists under such names as geyserite, fiorite and michaelite (see

OPAL) . Calcareous sinter is a deposit of calcium carbonate, exemplified by the travertine, which forms the principal building stone of Rome (Ital. travertino, a corruption of tiburtino, the stone of Tibur, now Tivoli) . The so-called " petrifying springs, " not uncommon in limestone-districts, yield calcareous waters which deposit a sintery incrustation on objects exposed to their action . The cavities in calcareous sinter are partly due to the decay of mosses and other vegetable structures which have assisted in its precipitation . Even in thermal waters, like the hot springs of Carlsbad, in Bohemia, which deposit Sprudelstein, the origin of the deposits is mainly due to organic agencies, as shown as far back as 1862 by Ferd . Cohn . Whilst calcareous deposits in the open air form sinter-like travertine, those in caves constitute stalagmite . Iron-sinter is a term sometimes applied to cellular bog iron-ore . (F . W .