PDF BOOK Gems; notes and extract.

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Gems; notes and extract. To download the book click the link below then click the PDF link on the left hand side of the page.

8 GEMS.

IV. Pearly brightness; that which resembles the
particular light of a pearl.

V. Silky brightness; that which gives the appearance
of silk-stuff.

The value of a gem depends principally 011 the
beauty of its colour. The colouring material is
generally composed of metallic oxides.

The wonderful variety of colours in the gems, which
more than all others resemble those of the solar
spectrum, gave rise to the diversity of names which
are often given to the same substance. The red
corundum is the oriental ruby ; the blue corundum is
the oriental sapphire; the yellow corundum is the
oriental topaz. The bluish-green emerald is now
called beryl. Quartz has many names; and more or
less value in its different colours.

There are crystals which not only have a varied
gradation of the same colour, but also present three
distinct colours.

I possess a quartz in which the central disc is red,
surrounded by a green zone, ending in a white band.
Corundums have been seen in which shone red, blue and
yellow ; and we sometimes see the tormaline variously
coloured, watered, and marked with strange figures.

In some gems the colour differs according to the
reflection or transmission of light. The opal with
reflected light is prismatic, and with transmitted light
it is whitish. The tormaline with reflected light is
red, blue, or some other equally bright colour, but
with transmitted light it is olive.

BY
AUGUSTO CASTELLAN! 1871

General Observalions . . 1

Hardness ..... 5

Specific Weight ... 6

Brightness, Colour, and

Transparency ... 7

Electricity 9

Fusion and Solution . .10

History and value of Gems . J.I

Adularia 17

Aquamarina 20

Agate 22

Alabastrite and Alabaster . 25

Almandine 27

Amazzonite 28

Amber 30

Amethyst 33

Apatite 35

Argirite 36

Asteria 38

Ivory 40

Aveuturine 42

Axinite 44

Beryl 45

Boort, or Knotty Diamond . 47

Cacholong 48

Calcedony 49

Calcedonyx 51

Carbon 52

Cyanite 54

Cymophaue 55

Link
http://www.archive.org/details/gemsnotesextract00castrich