It will be convenient now to describe the appearance of certain well-known minerals, as they are seen (A) in reflected light and (B) in thin sections in transmitted light, whilst the latter will be subdivided3 into 1 denoting the phenomena4 observed in ordinary light, and 2 in polarised light. To save repetition, the letters and figures will be used to denote the methods of examination as indicated.
Quartz5.—Present in nearly all rubber-bricks, and in the vast majority of common stocks, as well as in vitrified goods and fire-bricks. In the last mentioned, the grains are usually partially6 agglutinated, and are extremely minute.
A. As more or less rounded, or sub-angular fragments, white and crystalline, like clear window glass.
B. 1—Clear white, often broken up by thin hair-like lines running in various directions, and rows and patches of minute specks7, which, as previously8 remarked, have been shown to contain fluid, &c. 2—On revolving9 the129 stage of the microscope, the crystals are usually seen to present beautiful, clear transparent10 colours, which in characteristic sections are very vivid—red, blue, yellow, &c.
Flint.—Found in the same class of bricks as quartz.
A. Bluish horn colour; irregular fragments and splinters.
B. 1—Translucent; often melted more thoroughly11 than quartz in hard burnt bricks; colourless. 2—Opaque12 unless in some such form as chalcedony, when an extremely minute granular aspect results, becoming slightly transparent. Melted portions always opaque.
Felspar.—The alteration13 which the different kinds of felspar have undergone in a hard burnt brick, when present, render it almost impossible to recognise them specifically.
A. Milk white, or more rarely light pink; the mineral, even when red in the raw earths, becomes white on the application of moderate heat, as in the burning of common bricks. It is often closely fractured, and but rarely powdered.
B. The characteristic parallel lines of the triclinic varieties may often be observed, especially in rubber bricks; but great heat, such as leads to partial peripheral14 fusion15, frequently obliterates16 them to a large extent, and in a well-burnt brick it is quite impossible in the majority of cases to determine whether the felspars present are triclinic or monoclinic. More particularly is this the case when the mineral has been more or less decomposed17 prior to its having been burnt. The bulk of the fragments of the mineral can only be alluded18 to in the general term “felspars,” and in ordinary light these are opaque or “fleecy,” whilst in polarised light minute portions may be found to be slightly birefringent. In a130 decomposed state it forms a prominent constituent19 of brick-earths in the first place, and that is precisely20 the material which most readily agglutinates in presence of a suitable flux21. Crystallites are not uncommon22 in the melted peripheries23, as may be seen in a hard-burnt brick in ordinary light.
Mica24.—In minute flakes25, shining, or glistening26, and commonly black, silvery or bronze-coloured.
A. Detected at once by its thin shining scales, which frequently have not suffered much in the kiln except near the outside of the brick.
B. 1—The darker micas27 are usually citron coloured or light brown, and unless cut parallel to the cleavage of the mineral, exhibit a number of closely-set parallel lines, the fragments being much “frayed out” and “ragged” at the edges. 2—Using one nicol only, the mineral changes from dark to light on the revolution of the stage, and is said (in common with other minerals exhibiting a similar property) to be dichroic. With both nicols in position but little further difference is noted28, except that in changing tint29 the whole is darker. Vivid colours are not observed except in yellows and browns. Muscovite mica is often quite white and transparent.
Iron.—Common except in white bricks made from the purest china-clays.
A. Brown or reddish-brown specks; sometimes as blue black films in fire-bricks; dull and frequently powdery in common bricks. Surrounding, film-like, grains of mineral matter of which the brick is composed. A grain of quartz, for instance, is frequently seen enveloped30 by a film of red iron. Other metallic31 iron is more lustrous32 and whiter than magnetite when seen in reflected light, but such unaltered particles of the mineral131 could only occur in a brick that had not been subjected to great heat.
B. Opaque either in 1 or 2.
Iron Pyrite only occurs as such in bricks that have not been thoroughly burnt, or in common “baked” bricks. Higher temperatures lead to the separation of the iron from the sulphur and the general incorporation33 of both in the agglutination of the brick during partial fusion.
A. Brassy yellow particles.
B. Opaque both in 1 and 2.
Calcite.—Not found in burnt bricks, nor indeed in any except those that have been sun-dried, or have been subjected to very little heat. Small pellets of lime are of common occurrence in poorly-burnt bricks. In reflected light such pellets are generally of a dirty white tint; opaque in transmitted light.
Dolomite.—Practically the same observations apply as to calcite, crystals of dolomite not being found except in sun-dried bricks and the like. Under the action of much heat the mineral, like calcite, is reduced to lime.
Selenite.—This is not rare in the commoner class of bricks, though the application of much heat reduces it to the state of powder. In reflected light it is found to be present as extremely minute specks or “tears” of whitish powdery plaster. Opaque, of course, in transmitted light.
The description of the micro-appearance of many other minerals which occur but rarely in bricks does not fall within the scope of the present elementary treatise34; for practical purposes they may be ignored.
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1
dealing
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| n.经商方法，待人态度 | |
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2
kiln
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| n.（砖、石灰等）窑，炉；v.烧窑 | |
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3
subdivided
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| 再分，细分( subdivide的过去式和过去分词 ) | |
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4
phenomena
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| n.现象 | |
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quartz
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| n.石英 | |
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6
partially
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| adv.部分地，从某些方面讲 | |
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7
specks
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| n.眼镜；斑点，微粒，污点( speck的名词复数 ) | |
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8
previously
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| adv.以前，先前（地） | |
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9
revolving
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| adj.旋转的，轮转式的；循环的v.（使）旋转( revolve的现在分词 )；细想 | |
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10
transparent
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| adj.明显的，无疑的；透明的 | |
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11
thoroughly
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| adv.完全地，彻底地，十足地 | |
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12
opaque
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| adj.不透光的；不反光的，不传导的；晦涩的 | |
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13
alteration
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| n.变更，改变；蚀变 | |
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14
peripheral
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| adj.周边的，外围的 | |
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15
fusion
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| n.溶化；熔解；熔化状态，熔和；熔接 | |
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16
obliterates
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| v.除去( obliterate的第三人称单数 )；涂去；擦掉；彻底破坏或毁灭 | |
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17
decomposed
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| 已分解的，已腐烂的 | |
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18
alluded
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| 提及，暗指( allude的过去式和过去分词 ) | |
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19
constituent
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| n.选民；成分，组分；adj.组成的，构成的 | |
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20
precisely
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| adv.恰好，正好，精确地，细致地 | |
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21
flux
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| n.流动；不断的改变 | |
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22
uncommon
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| adj.罕见的，非凡的，不平常的 | |
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23
peripheries
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| n.外围( periphery的名词复数 )；边缘；周围 | |
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24
mica
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| n.云母 | |
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25
flakes
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| 小薄片( flake的名词复数 )； （尤指）碎片； 雪花； 古怪的人 | |
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26
glistening
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| adj.闪耀的，反光的v.湿物闪耀，闪亮( glisten的现在分词 ) | |
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27
micas
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| n.云母( mica的名词复数 ) | |
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noted
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| adj.著名的，知名的 | |
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29
tint
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| n.淡色，浅色；染发剂；vt.着以淡淡的颜色 | |
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30
enveloped
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| v.包围，笼罩，包住( envelop的过去式和过去分词 ) | |
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31
metallic
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| adj.金属的；金属制的；含金属的；产金属的；像金属的 | |
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32
lustrous
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| adj.有光泽的；光辉的 | |
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33
incorporation
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| n.设立，合并，法人组织 | |
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34
treatise
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| n.专著；(专题)论文 | |
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