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Updated: May 2, 2025
Among them are amethyst, and other varieties of crystal, of quartz, henlandite, stibite, analcine, chabasie, albite, nesotype, silicious sinter, and so on. Pray do me the favour to accept this amethyst. I have several others of equal size and beauty, and it is of no use to me."
The beautiful map of Roto Mahana on an enlarged scale by Hochstetter shows no fewer than ten large sinter terraces descending towards the margin of this lake, besides several mud-springs, fumaroles, and solfataras.
Quartz, dense and milky, also in quartz of nearly every colour and appearance, saccharoidal, crystalline, nay, even in clear glass-like six-sided prismatic crystals, and associated with silver, copper, lead, arsenic, iron as sulphide, oxide, carbonate, and tungstate, antimony, bismuth, nickel, zinc, lead, and other metals in one form or another; in slate, quartzite, mica schist, granite, diorite, porphyry, felsite, calcite, dolomite, common carbonate of iron, siliceous sinter from a hot spring, as at Mount Morgan; as alluvial gold in drifts formed of almost all these materials; and once, perhaps the most curious matrix of all, a small piece of apparently alluvial gold, naturally imbedded in a shaly piece of coal.
Numerous veins of jasper and of siliceous sinter, occurring on the summit of this same hill, show that there has been some abundant source of silica, and as these plate-like veins differ from the trachyte only in their greater hardness, brittleness, and less easy fusibility, it appears probable that their origin is due to the segregation or infiltration of siliceous matter, in the same manner as happens with the oxides of iron in many sedimentary rocks.
An advance boring on the 3000 ft. level of the Yellow Jacket struck a powerful stream of water at 3065 ft. A spring on the 2700 ft. level of the Yellow Jacket which showed a temperature of about 150 degrees F., was found to be depositing a sinter largely composed of carbonates."
But the action was hydrothermal, just such as was seen in course of operation in New Zealand a few years ago when, in the Rotomahana district, one could actually see the growing of the marvellous White and Pink Terraces formed by the release of silica from the boiling water exuding from the hot springs, which water, so soon as the heat and pressure were removed, began to deposit its silica very rapidly; while at the Thames Gold-field, in the same country hot, silicated water continuously boiled out of the walls of some of the lodes after the quartz had been removed and re-deposited a siliceous sinter thereon.
Hot springs rising through alkaline siliceous rocks, such as lavas, often deposit silica in a white spongy formation known as SILICEOUS SINTER, both by evaporation and by the action of algae which secrete silica from the waters. It is in this way that the cones and mounds of the geysers in the Yellowstone National Park and in Iceland have been formed.
The entire cranium, including the face, is covered with a thick layer of sinter, which gives it the appearance of belonging to the class of skulls with Leontiasis ossea. It is, in fact, of good size, but through the incrustation it is increased to gigantic proportions. It is true, likewise, that it has a much flattened, broad and compressed form.
Six hours westward by water, and one hour S.S.W. on foot, brought us to the Visita Bícul, surrounded by a thousand little limestone hills; from which we ascended by a staircase of sinter in the bed of a brook, to a small cavern tenanted by multitudes of bats, and great long-armed spiders of the species Phrynus, known to be poisonous.
But the largest and most celebrated of all the sinter terraces has within the last few years been buried from view beneath a flood of volcanic trass, or mud, an event which was as unexpected as it was unwelcome.
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