. Transactions. ll percentage of the alumina in the ore is present as hydratedaluminum silicate, as shown by the low silica content; the remainderof the alumina has been calculated as bauxite; possibly other forms ofhydrated aluminum oxide are also present. After allowing for thechromite, the remainder of the ferrous oxide has been calculated asmagnetite. That the chromium is present as chromite was determinedby treating the material with hydrochloric acid and then separating theblack metallic particles in the residue. These gave the typical emerald-green bead of chromium with salt of phosphor
. Transactions. ll percentage of the alumina in the ore is present as hydratedaluminum silicate, as shown by the low silica content; the remainderof the alumina has been calculated as bauxite; possibly other forms ofhydrated aluminum oxide are also present. After allowing for thechromite, the remainder of the ferrous oxide has been calculated asmagnetite. That the chromium is present as chromite was determinedby treating the material with hydrochloric acid and then separating theblack metallic particles in the residue. These gave the typical emerald-green bead of chromium with salt of phosphorus. After allotting asmall percentage of ferric oxide to magnetite, the remainder was dis-tributed between limonite and goethite in such proportions as to accountfor the remainder of the combined water. It is probable that at least aportion of the ferric oxide and water are present in other combinations,but it is not supposed that hematite occurs to any extent in the sampleon account of the absence of red Fig. 8.—Section op limonite boulder, direct light. In addition to the loose earthy material, numerous boulders andmasses of hard ore occur scattered over the limonite area. Theseboulders retain the porous structure of the soft ore, but contain littleveinlets running in all directions and filled with the botryoidal form oflimonite with varnish-like luster. These boulders range in diameterfrom a few inches up to several feet; apparently they have been washedout of the upper layers of loose material. A thin section from such a boulder, under the microscope, showed thatthe hydrated iron oxide is present in two forms, cryptocrystalline andamorphous. The former variety retains the structure of the serpentine,while the amorphous has been deposited afterward in little veinletsrunning in every direction throughout the former; these show a banded 106 LIMONITE DEPOSITS OF MAYAGUEZ MESA, PORTO RICO structure. Small grains of magnetite and chromite appear here and there,just as i
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Keywords: ., bo, bookcentury1800, bookdecade1870, booksubjectmineralindustries
