or LAPIS LAZULI, a species of zeolite belonging to the class of argillaceous earths. See Clay, no. 7. It is of a blue colour. That which is of a fine blue inclining to purple, has obtained the name of Oriental; but the pale blue is less esteemed. It is frequently variegated with yellow, and white shining veins and speckles; which the common people take for gold and silver, though they are in truth nothing but marcasites. The lapis lazuli has the following properties: 1. It retains its blue colour for a long time in a calcining heat; but changes at last to a brown. 2. It melts easily in the fire to a white frothy slag; which puff up greatly when exposed to the flame of a blow-pipe; but with a strong heat in a covered vessel, it becomes clear and solid, with blue clouds in it. 3. It does not ferment with acids; but, if boiled with oil of vitriol, it slowly dissolves, and loses its blue colour. On adding a solution of fixed alkali, it precipitates a white earth, which being scorified with borax, yields a silver coloured regulus, varying in bigness according to the different specimens of the stone. 4. By scorification with lead, it yields silver, sometimes in the quantity of two ounces to a hundred weight of the stone. 5. Oil of vitriol discovers the presence of silver more certainly in lapis lazuli than spirit of nitre. 6. On adding spirit of sal ammoniac to any solution either of crude or calcined lapis lazuli, no blue colour is produced; a certain proof that it does not depend on copper; which is further confirmed by the fixity of the blue colour in the fire, and the colour of the flag or glass. 7. It is somewhat harder than the other kinds of zeolite, but does not approach to the hardness of quartz or other siliceous stones in general; for the purest and finest lapis lazuli may be rubbed into a white powder by means of steel, though it takes a polish like marble. 8. When perfectly calcined, it is a little attracted by the loadstone; and when scorified with lead, the flag becomes of a greenish colour, not like that produced by copper, but such as is always produced by iron mixed with a calcareous substance.

Mongez informs us, that some of the parts of lapis lazuli will strike fire with steel. According to Cronstedt, it is seldom found pure; but generally full of veins of quartz, limestone, and marcasite; but for the experiments by which the above mentioned qualities were determined, the purest pieces were picked; such as had been examined through a magnifying glass, and judged as free from heterogeneous mixture as possible. Our author expresses a wish that such as are in possession of any quantity of the stone would make farther experiments, in order to determine what substance it is which produces the blue colour so constant in the fire, since it cannot depend either on copper or iron; for though these metals, on certain occasions, give a blue colour, yet they never produce any other but what instantly vanishes in the fire, and is destroyed by means of an alkali. "What is mentioned in several books (says he) can by no means be objected here; since in these processes the silver employed is mixed with copper and other substances which contain a volatile alkali, whereby the blue colour is produced."

In the year 1761 M. Margraaf published some experiments on the lapis lazuli; in which he agrees in a great measure with Cronstedt. According to him, the lapis lazuli does not contain any copper; but he found in it a calcareous and gypseous substance, though he took care to pick out the very purest bits he could find. Engelstrom, however, is of opinion, that the calcareous substance is not essential to lapis lazuli; as Cronstedt says, that the lapis lazuli he tried did not ferment with acids. He farther mentions, that when dissolved in any of the mineral acids, it always turned Leachlade, them into a jelly. Some of his experiments also seem to indicate, that all kinds of lapis lazuli do not contain silver, though many of them do.

The lapis lazuli is found in many parts of the world; but that of Asia and Africa is much superior both in beauty and real value to the Bohemian and German kind, which is too often sold in its place.