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Hardness 4, specific gravity 2.3; it generally occurs in small crystals, but more frequently in a crumbly, chalky mass, which it becomes upon exposure to the air. The crystals are generally transparent and frequently tinged yellow in color. It gelatinizes by boiling with acid, and after intumescing before the blowpipe, fuses to a frothy mass.
A silicate which gelatinizes on treatment with acids should be mixed first with a little water, and the strong acid added in small portions with stirring, otherwise the gelatinous silicic acid incloses particles of the original silicate and prevents decomposition. The water, by separating the particles and slightly lessening the rapidity of action, prevents this difficulty.
A flocculent residue will often remain after the decomposition of the fused mass is effected. This is usually partially dehydrated silicic acid and does not require further treatment at this point. The progress of the dehydration is indicated by the behavior of the solution, which as evaporation proceeds usually gelatinizes.
After a long boiling with nitric acid it gelatinizes, but it foams up and fuses to a transparent glass before the blowpipe. A little stilbite may often be found on the dumps. Laumonite occurs in very small quantities on calcite or apopholite, and can hardly be expected to be found on the trip; but as it might be found, I will detail some of its characteristics.
The fibers are very tightly packed together, as are also the groups; they are very tough individually, and have a hardness of 4, and a specific gravity of about 2.5. It gelatinizes on boiling with acid, and a fragment may be readily fused in the blowpipe flame, yielding a transparent globule.
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