Ca[CO 3 ] is a homomorphic image with calcite .

[Chemical composition] Ca is often replaced by Sr, Pb, Zn, and TR. In addition, there are Mg, Fe, Al, etc., but the content is generally low. Known variants lead aragonite, aragonite zinc, strontium aragonite, aragonite rare earth.

[crystal structure] orthorhombic system 360 screenshot 20170722103458977 a 0 = 0.495 nm, b 0 = 0.796 nm, c 0 = 0.573 nm; Z = 4. The aragonite structure is found in the overview section of Mineralogy Chapter 22.

[Form] Crystals are often columnar and spear-shaped (Figure H-8), but they are rare. Often (110) into twin or triple crystal, triple crystals often appear pseudo hexagonal symmetry. The aggregates are often fibrous, columnar, cluster-like, hull-like, stalactite, coral, scorpion, bean, and globular (Figure H-9). The pericarp portion of the inner wall of most mollusk shells is made up of extremely fine flaky aragonite arranged in parallel along the shell surface.

Picture 67

Figure H-8 Crystal and Twin Crystals of Aragonite

(quoted from Pan Zhaoyu, 1993)

(a) (b) (c) single crystal, (d) twin crystal oblique column: m{110}, k{011}, i{021}, g{061}; parallel double-sided: b{010}, c{001}; orthorhombic double cone: p{111}, r{121}

Picture 68

Figure H-9 Crystal aggregate of aragonite

[Physical properties] usually white, yellowish white, sometimes light green, gray, etc.; transparent; glass luster, fracture is grease luster. No cleavage, or sometimes see {010} not completely to moderate cleavage; shell-like fracture. Hardness 3.5 to 4.5. The relative density is 2.9 to 3.3, and the relative density of Sr and Ba in the composition is increased.

Picture 69

Figure H-10 The approximate stability range of calcite and aragonite

(quoted from Pan Zhaoyu, 1993)

[genesis and production] Aragonite is usually formed under low temperature hydrothermal and exogenous conditions, and it is one of the low temperature minerals. Crystallized in hydrothermal deposits, modern hot springs, and geysers. The presence of Sr and Mg salt impurities in the solution is beneficial to the formation of aragonite. Aragonite is unstable and often converted to calcite (a portrait of aragonite). According to synthetic mineral data, aragonite is formed at a higher pressure than calcite (Figure H-10).

[Identification characteristics] Aragonite is similar to calcite, and HCl is vigorously foamed. However, aragonite does not have rhombohedral cleavage, and the crystal form is columnar and lancelike; the relative density and hardness are slightly larger than calcite. Boiled in a cobalt nitrate solution, the calcite powder is only slightly cyan, and the aragonite is rich in red and purple.

[Main use] There is little distribution and almost no industrial value.

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 The whole set of equipment consists of four parts:

1.incineration system

2. Purification system
3. Carbonization system
4. Control system

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