The lapis-lazuli, sometimes called “azure stone,” is almost always blue, though often containing streaks of white and gold colour, the latter of which are due to the presence of minute specks or veins of iron pyrites, the former and colourless streaks being due to free lime, calcite, and other substances which have become more or [...]
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The word “electricity” is derived from the Greek “elektron,” which was the name for amber, a mineralised resin of extinct pine-trees. It was well-known to the people of pre-historic times; later to the early Egyptians, and, at a still later date, we have recorded how Thales -the Greek philosopher, who lived about the close of [...] Hardness is perhaps one of the most important features in a stone, especially those of the “gem” series, for no matter how colour, lustre, general beauty and even rarity may entitle a stone to the designation “precious,” unless it possesses great hardness it cannot be used as a gem or jewel. Consequently, the hardness of [...] Color is one of the most wonderful effects in nature. It is an attribute of light and is not a part of the object which appears to be coloured; though all objects, by their chemical or physical composition, determine the number and variety of vibrations passed on or returned to the eye, thus fixing their [...] By cleavage is meant the manner in which minerals separate or split off with regularity. The difference between a break or fracture and a “cleave,” is that the former may be anywhere throughout the substance of the broken body, with an extremely remote chance of another fracture being identical in form, whereas in the [...] |
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