WERNER.
A. Dotted. In this variety, dots or small spots are ir regularly dispersed over a surface which has a differ ent colour from the spots. It occurs frequently in serpentine, but seldom in other minerals.
B. Spotted. If the spots are from a quarter of an inch to an inch in diameter, and the basis or ground still visible, it is said to be spotted. It is either round and regularly spotted, or irregularly spotted. The first occurs in clay-slate ; the second in marble.
C. Clouded. Here no basis is to be observed ; the boundaries of the colours are not sharply marked, and the spots run into each other. It occurs in mar ble and jasper.
D. Flamed. When the spots are long and acuminated, and arranged according to their length, the flamed delineation is formed. It has still a basis. It occurs in striped jasper, marble, &c.
E. Striped. Consists of long and generally parallel stripes, that touch each other and fill up the whole mass of the stone, so that it has no ground. It pre sents two varieties.
a. Straight striped, as in striped jasper and variegated clay.
b. Ring-shaped, occurs in Egyptian jasper.
F. Veined. Consists of a number of more or less deli cate veins crossing each other in different directions, so that it is sometimes net-like. ‘Ve can always dis tinguish a base or ground. Examples, black marble veined with calcareous spar or quartz, jasper and serpentine.
G. Dendritic. Represents a stem uith branches, on a ground. Examples, steatite and dendritic calce dony.
II. Ruiniform. Resembles ruins of buildings. It cc curs in Florentine marble, which is from this circum stance called laniscape marble.
III. The Play of the Colours.
If we look on a mineral which possesses this proper ty, we observe, on turning it slowly, besides its common colours, many others, which are bright, change very rapidly, and are distributed in small spots or patches. A strong light is required, in order to see this appear ance distinctly, and it never occurs in opaque or feebly translucent minerals. We observe it in the diamond when cut, and in precious opal.
IV. The Changeability of the Colours When the surface of a mineral, which we turn in different directions, exhibits, besides its common colours, different bright colours, that do not change so rapidly, are fewer in number, and occur in larger patches than in the play of the colour, it is said to exhibit what is called the changeability of the colours. The change ability of colour is seen only in particular directions, the play of colour in all directions.
We distinguish two kinds of this phenomenon.
A. That which is observed by looking in different posi tions on the mineral, as in Labrador felspar.
B. That observed by looking through it, as in the com mon opal, which shows a milk-white colour when we look on its surface, but when held between the eye and the light is vine-yellow.
V. The Iridescence.
When a mineral exhibits the colours of the prism or the rainbow, arranged in parallel, and sometimes vari ously curved layers, it is said to be iridescent. It is to be observed by 4. Looking on the mineral only, as in precious opal, adularia, &c.
B. Both by looking on the mineral and through it, as in calcareous spar, crossed by thin veins, some arrago nites, rainbow calcedony, and some amethysts.
VI. Tarnished Colours.
A mineral is said to he tarnished, when it shows on its external surface, or on that of the distinct concre tions, fixed colours different from those in its interior or fresh fracture.
There are simple or variegated tarnished colours.
a. Simple.
a. Grey,—white cobalt.
p. Black,—native arsenic.
y. Brown.—magnetic pyrites.
Reddish,—native bismuth.
b. Variegated.
The variegated or party-coloured, are distinguished according to the intensity of their basis. Of these tit( following are enumerated in the tabular view.
x. Pavonine, or Peacock-tail tarnish. This is at assemblage of yellow, green, blue, red, and brown colours, on a yellow ground. The colours are nearly equal in proportion, and are never pre. cisely distinct, but always pass more or less intc one another. Example, copper-pyrites.
p. Iridescent, or Rainbow. In this variety the co. lours are red, blue, green, and yellow, on a grey. ground. It is more beautiful and brighter than the preceding. The radiated grey antimony o Felsobanya in Hungary, and the specular iron ore, or iron-glance of Elba, are often beautifully iridescent.
7. Columbine, or pigeon-neck tarnish. The colour! are the same as in the preceding, with this differ• once, that the tints of colour are paler, and the red predominates. Examples, native bismuth o Schneeherg.
(3`. Tempered-steel tarnish. It consists of very pal( blue, red, green, and very little yellow, on a grey ground. Example, grey cobalt.
VII. The Permanent Alterations.
These must not be confounded with the tarnished co. lours. The tarnish occurs only on the surface; the per. manent alteration, on the contrary, proceeds by degree: through the whole mass of the mineral. This change takes place more or less rapidly in different minerals. The colours either become paler, when they are said to fade, or they become darker, and pass into other varie ties. Thus chrysoprase, rose quartz, and red cobalt ochre become paler ; whereas sky-blue fluor-spar be comes green, pearl-grey corneous silver sometimes changes to brown, and lastly into black, and earthy blue iron changes from white, through different varieties of blue, to indigo-blue.