258 



THE POPULAR EDUCATOR 



SULPHUR is found in the neighbourhood of volcanoes mixed 

 with the earth. When crystallised it is trimetric, usually in 

 octahedrons, but more frequently it is massive. Our chief 

 European supply is obtained fr>_>m the valley of Noto and Maz- 

 zaro, in Sicily. However, large quantities are procured from 

 copper and iron pyrites. Sulphur is dimorphous, for when 

 artificially crystallised it appears in the monometric system. 



CARBON. This element is found native in three distinct con- 

 ditions Diamond, Graphite or Plumbago, and Anthracite. 



The Diamond crystallises in the monometric system ; usually 

 in octahedra and dodecahedra, which have very often curved 

 t'aces. It exhibits a very perfect octahedral cleavage. H. = 10 ; 

 sp. gr. = 3'48 3'55. It is almost pure carbon. When heated 

 to redness in a cage of platinum wire, and plunged into a jar of 

 oxygen, the gem burns into carbonic acid gas, leaving sometimes 

 a little silica ash in the cage. There is every reason to believe 

 the diamond was formed in sandstone rocks, called Itacolumite, 

 from carbon accumulated by animal or vegetable life. It is now 

 found in the loose soil and gravel which the degradation of such 

 rocks has produced. It is yielded by such deposits in Brazil, 

 in North Carolina, in the Ural, and near Delhi, and Golconda. 

 Slaves are employed to wash the gravel, and an experienced eye 

 readily picks out any diamonds which may be in the cradle. It 

 usually appears like a broken lump of glass, but 'has a more 

 lustrous glitter. To cut it, in order that its great refractive 

 and dispersive power may be exhibited to advantage, it is fitted 

 with a metallic cement into a handle, and then pressed down 

 upon a diso of steel about six or eight inches in diameter, which 

 rapidly revolves horizontally. The steel is impregnated with 

 diamond dust, and this wears a facet. Great art is required, 

 for there is a grain in the diamond, and if the stone be set so 

 that the plate attempts to cut it against the grain, the steel is 

 cut and not the diamond. Diamond-cutting was first attempted 

 in Europe by Louis Berquen, a citizen of Bruges, in 1456, and 

 the Dutch monopolised the trade until very recently. Before 

 the introduction of machinery the process was most tedious. 

 Two diamonds set in metallic cement were rubbed by hand one 

 against the other until a facet was worn in each. 



Diamonds are sold by weight. A carat is the unit employed, 

 and is about 3 grains troy. The term is derived from the 

 name of a bean used in Africa to weigh gold. These beans were 

 carried to India, and there were employed to weigh diamonds. 

 To determine the value of a diamond, double the weight in 

 carats, and multiply the square of the product by 2. Thus a 

 cut diamond weighing one carat would be worth .8 ; one 

 weighing ten carats, ,800. The largest diamond on record 

 belonged to the Great Mogul. It was found in 1550, in the 

 mine of Colone. It weighed in its rough state 900 carats, but 

 in cutting was reduced to 272J- carats. 



Upon the annexation of the Punjaub in 1850, the Queen of 

 England became possessed of the Koh-i-Noor, a diamond whose 

 original weight was 793 carats, but which has been reduced by 

 repeated cuttings to its present weight of 103jf carats. The 

 Koh-i-Noor has a long history. We first hear of it in the year 

 50 A.c., when it was in the possession of the Rajah of Mjayin ; 

 and since that remote date it has been worn by princes in- 

 namerable, and has ornamented idols many, until, to-day, it 

 has the honour of being worn by our Queen. Our illustration 

 shows this jewel, with two smaller diamonds, as it appeared in 

 the Exhibition of 1851. Below is the gold-work in which it was 

 set. Since this time it has been re-cut. 



The Eussian diamond was purchased by Catherine II. It was 

 stolen from a Brahminican idol, to whom it was an eye, by a 

 French grenadier. It weighs 194 carats, and has in its time 

 been sold for .90,000 and an annuity of .4,000 a-year ! 



Graphite or Plumbago the blacklead of pencils is pure 

 carbon ; occasionally it contains a little iron. It is found, when 

 bearing any crystalline structure, in short, tabular, prismatic 

 crystals, which, being six-sided, belong to the hexagonal system. 

 It is found in metamorphic rocks, and is believed to be beds of 

 coal which have undergone metamorphism. 



Anthracite is a term used to express coal which does not con- 

 tain any bitumen. It is the amorphous form of native carbon 

 the, charcoal of Nature. 



2. OXYGEN COMPOUNDS. 



An oxide is formed when oxygen enters into chemical com- 

 bination with an element. Thus the rust of iron is the oxide of 



that metal a compound of the two elements, iron and oxygen. 

 There are many such oxides in the mineral kingdom. 



QUARTZ is the oxide of silicon. When pure, as rock crystal 

 it occurs in the hexagonal system, as six-sided prisms terminated 

 by six-sided pyramids, as is shown in Fig. 30 (p. 176). Quartz. 

 is the most widely distributed mineral, being almost the sole 

 component of sandstone. H. = 7. It scratches glass. Sp. gr. 

 = 2'6 2 - 7. Acids have no action upon it. By these characters 

 it is readily distinguished. It is one of the three constituents 

 of granite. When coloured by various metallic oxides it assumes 

 forms known by the names 



Amethyst, violet quartz. 



Chalcedony, opaque quartz. 



Cornelian, red chalcedony. 



Agate consists of alternate layers of pure quartz and chalce- 

 dony. 



Onyx is agate which has the layers evenly and horizontally 

 arranged, and is much used for cutting cameos. 



Cat's-eye is translucent chalcedony which throws reflected 

 light from its interior. This is due to filaments of asbestos 

 which are distributed through it. 



Flint is massive silica which occurs in nodules in chalk. 



Jasper is opaque quartz, coloured yellow and red by peroxide 

 of iron. It is found with the bog iron ore of Germany, among 

 the pebbles of the Nile, and some few other places. 



Bloodstone or Heliotrope is a variety of silica which is green 

 and slightly translucent, containing spots of red, bearing some- 

 resemblance to stains of blood. 



Opal is quartz containing four to ten per cent, of water in com- 

 bination ; its peculiarity is that it presents an internal play of 

 colours when turned in the hand. It is found in cavities in the 

 Trachyte rocks in Hungary. Hyalite is a colourless variety 

 found in Mexico. 



Siliceous Sinter has often the composition of opal. It is de- 

 posited by the Geysers of Iceland. 



Tabasheer is a most peculiar variety, being an aggregation of 

 silica, which forms in the joints of the bamboo. 



CORUNDUM is an oxide of aluminium, containing two atoms of 

 the metal and three of oxygen. It occurs massive in Saxony, 

 and from this source is derived for commerce, and sold as emery. 

 It is almost as hard as the diamond. When transparent it is 

 precious. In this state it is found in the alluvial deposits of 

 Ceylon, China, and Siam. If blue, it is Sapphire, a gem which 

 rivals the diamond in value ; when red, it is Ruby, but then its 

 composition is not so simple, as it contains one of the oxides of 

 chromium. 



OXIDES OF IRON. Bed Hematite is a sesquioxide of iron 

 that is, it has a similar composition to corundum, two atoms of 

 the metal to three of the gas. As Specular Iron Ore, it has a 

 perfectly metallic lustre ; as Micaceous Iron, it is foliated ; as 

 Red Hematite, it is massive, or in mammillary masses, which 

 show a fibrous structure, and from its appearance has deserved 

 the name of Kidney ore. 



Brown Hematite is a variety of the red hematite, which is 

 associated with water ; it frequently occurs as incrustations 

 attached to other rocks. 



Magnetic Iron Ore contains three atoms of iron and four of 

 oxygen ; it is the only oxide of iron capable of magnetisation, 

 and is therefore affected by the earth's magnetism, producing 

 the " lodestone." 



OXIDES OF COPPER. The Red Copper Ore is a suboxide of 

 the metal, containing two atoms of the metal and one of 

 oxygen. It is often found in regular octahedrons of the mono- 

 metric system. Its colour is deep red; lustre, adamantine. 

 H. = 3-5 4; sp. gr. = 6. 



Black Copper Ore or Tenorite is the protoxide of copper, con- 

 taining one atom of the metal united with one of oxygen. It 

 generally occurs in dull black masses, and in veins traversing 

 other copper ores ; occasionally it is found in crystals which are 

 cubes. 



THE OXIDE OF TIN. Tinstone is the source of the metal. 

 When crystallised it appears in the dimetric system in modified 

 square prisms, terminated by the solid angle of the octahedron. 

 Tinstone has been mined in Cornwall for ages. The great 

 mariners of the ancient world the Phoenicians dared to pass 

 the Pillars of Hercules, and come to Britain for this ore. It is 

 found in small quantities in Saxony, Austria, and Finland ; but in 

 the East Indies there are some valuable deposits. The island of 



