Compared with artificial stone, natural marble is easy to be polluted and not resistant to corrosion and scratch. Why are people willing to pay a high price for so many defects? Yes, every piece of marble is different. But is a unique stone worth cherishing, or possession of it worth showing off? Not so, because your minds follow your eyes.
Different from artificial stones such as rock slabs, the pattern of natural stones is not a two-dimensional graphic printed on the surface, but a three-dimensional pattern with depth and perspective. Different mineral components overlap, inlay and penetrate to each other’s. Even if they are cut into a group of thin sheets with a thickness of 1mm, each pattern is different. Not only that, the flash refracted by the mineral crystals in the shape of granular, crystal cluster fiber, spreads like pearl, like shell, like silk. When they are extended on the surface, they change with the angle of light projection and the line of sight of the observer. What's more, transparent mineral crystals make patterns up to one-centimeter depth. This makes it like being given life, breathing every inch. If you have been enchanted by the rock slab, when you compare it with marble, you will realize how dull, lifeless and lack of flexible it is without a sense of hierarchy. The difference between them is like a vase twisting its waist, pretending to be amorous feelings, and the smile of a fair lady who is full of poetry and books.
A sample of marble cut to a thickness of 2 mm. The light projected from behind shows that most of its area is translucent. In fact, the famous Italian marble Carrara White, even if it is up to 1.5cm thick, can see the penetrating gentle backlight when facing away from the sun.
The characteristic eddies and textures of many marbles are usually caused by various mineral impurities, such as clay, silt, sand, iron oxide or flint, which initially appear in limestone in the form of particles or layers.
Part of Van Gogh Gold marble, in which the light transparent part is calcite.
Although this article is not a popular science article of geologists or mineralogists, for the sake of illustration, we take granite (igneous rock) commonly used as building exterior wall and marble (metamorphic rock) used as indoor floor as examples. Understanding the composition and structure of natural stones will help you understand where these flashes and transparency come from and why uncertainty brings unspeakable pleasure to your vision.
Granite is mainly composed of feldspar, quartz, mica, amphibole and pyroxene dominated by chemically stable silicate. The main components of marble are calcite and dolomite dominated by carbonate which is easy to be acid eroded. However, in the geological movement, the deposits are also mixed with clay, silt, animal and plant fossils, feldspar and amphibole.
The proportion of feldspar in the earth's crust is as high as 60%, which can appear in igneous rock, metamorphic rock and sedimentary rock. Feldspar is usually milky white, but it is often dyed yellow, brown, light red, dark gray and other colors due to a variety of impurities. Some can also have beautiful color change or halo. The halo effect of feldspar shows that when the sample is rotated to a certain angle, it can display blue, green, orange, yellow, golden yellow, purple and red halos. Feldspar has two groups of complete cleavage, with an angle of 90 ° (monoclinic system) or nearly 90 ° (87 °) in between.
set of various feldspar stones
Part of the blue pearl labradorite, the feldspar shows blue halo color. It displays various shapes and colors from different observation angles. This 1 cm thick sample is mostly transparent.
Quartz is usually in the form of crystal cluster, material and massive aggregate. The pure quartz is colorless and transparent. It shows various colors due to the presence of trace pigment ions, subdivided loose inclusions, or color centers, and reduces the transparency. It has glass luster and the fracture is greasy luster. Hardness 7, no cleavage, shell fracture.
A variety of quartz crystals from Moravian Highlands including citrine, smokey quartz and morion.
Mica has perfect cleavage and can be stripped. Muscovite flakes are generally colorless and transparent, but they are often dyed with colors such as green, brown, yellow and pink; Glass luster, cleavage surface is pearl luster.
set of common mica sheets
Amphibole is an important and widely distributed rock forming mineral, which can be found in both igneous and metamorphic rocks. The aggregate is granular, fibrous, radial, etc. Generally dark, from green, brown, brown to black. Glass luster. The intersection angles of the two groups of moderately developed cleavage planes are 124 ° and 56 °. Amphibole, sodium amphibole, tremolite and actinolite are sometimes fibrous aggregates with silk luster.
set of various amphibole stones
Amphibolite rock under the microscope
Pyroxene is called jadeite. Because the texture of emerald is the best, it has the elegant name of emerald in China. It has a faint crystal structure, hard and high texture, with the luster of glass, clear and crystal. Emerald green, apple green, snowflake white and delicate Lavender are typical colors of pyroxene. Most ancient Chinese jade articles are amphibole products.
Abstract micrograph of the mineral olivine pyroxenite, viewed with a polarizing microscope at 100x.
Calcite is a kind of calcium carbonate mineral, which is widely distributed. Calcite crystals have various shapes, and their aggregates can be clusters of crystals, granular, massive, fibrous, stalactite, earthy and so on. Many square fragments can be obtained by knocking calcite. The color of calcite varies according to the impurities contained in it, such as light yellow, light red, brown black, etc. when containing iron and manganese, but it is generally white or colorless. Calcite is widely distributed in nature.
In shallow waters or lakes, it is often deposited to form vast limestone layers. Groundwater can dissolve limestone and reform calcite, such as stalactite, stalagmite, and tufa, etc. The underground water moving in the soil often forms calcite nodules distributed along a certain horizontal plane near the phreatic surface. Calcite often accounts for about 80% of the carbonates formed by magmatism.
In addition, calcite is also used as the cement of clastic sedimentary rocks, and the minerals participate in various rocks from the result of alteration of basic magmatic rocks. Due to groundwater activities, calcite veins are often filled in the fissures of various rocks.
In the process of regional metamorphism or contact metamorphism, the calcite in the limestone formed by sedimentation often recrystallizes to form a calcite aggregate with coarse grain - marble.
Quartz and Calcite Geode with Iron Deposits
The resulting marble is usually inlaid with interlocking carbonate crystals. The original sedimentary structure and structure of primitive carbonate rocks (protoliths) have usually been modified or destroyed.
Pure white marble is the result of metamorphism of very pure (lack of silicate) limestone or dolomite protolith. Green is usually caused by serpentine formed from magnesium rich limestone or dolomite containing silica impurities. These different impurities are mobilized and recrystallized by strong pressure and heat of metamorphism.
limestone with calcite
Petrographic thin section under the microscope and with polarized light. Thin sections are geological samples for microscopy. The rock is a fossil rich limestone of Miocene age from Europe.
Dolomite crystal belongs to carbonate mineral of cubic system. The crystal structure of dolomite is similar to that of calcite. The crystal form is rhombohedron, and the crystal surface is often bent into saddle shape. Flake bicrystals are common, mostly in block and granular aggregates. Pure dolomite is white, sometimes grayish green, grayish yellow, pink and other colors due to other elements and impurities, with glass luster.
Dolomite Mine Excavation.