Romanechite

Roman candles Roman chamomile oil Romanechite Romazicon Romet-30 Romet-B... 

Pyrolusite is a black, opaque mineral with a metallic luster and is frequendy soft enough to soil the fingers. Most varieties contain several percent water. Pyrolusite is usually a secondary mineral formed by the oxidation of other manganese minerals. Romanechite, a newer name for what was once known as psilomelane [12322-95-1] (now a group name) (7), is an oxide of variable composition, usually containing several percent water. It is a hard, black amorphous material with a dull luster and commonly found ia the massive form. When free of other oxide minerals, romanechite can be identified readily by its superior hardness and lack of crystallinity. 

Figure 7. Crystal structures of (a) hollandite, (b) romanechite (psilomelane), and (c) todorokite. The structures arc shown as three-dimensional arrangements of the MnO() octahedra (the tunnel-tilling cations and water molecules, respectively, are not shown in these plots) and as projections along the short axis. Small, medium, and large circles represenl the manganese atoms, oxygen atoms, and the foreign cations or water molecules, respectively. Open circles, height z. = 0 fdled circles, height z = Vi.

Rolling ball viscometers, 21 738 Roll mills, 16 722 Rolls, high pressure, 16 612-613 Romanechite, 15 540 Romascone, 24 571 Romet-30/Romet-B. See Ormetoprim ROMP catalysts, 17 707, 708 ROM polymers. See also Ring-opening metathesis (ROM) polymers, 26 947-948 Roof coatings... 

Cryptomelane Psilomelane Romanechite Ki-2Mri80-i6 XH2O (Ba,K,Mn,Co)3(0,OH)6MnsOi6 ... 

Turner, S. Post, J. E. (1988) Refinement of the substructure and superstructure of romanechite. Amer. Mineral., 73,1155-61. 

Figure 25 Schematic diagram of tmmel structures built from rutile chains 1x1, rutile 2x2, hollandite 2x3, romanechite 3x3, todorokite. (Reprinted with permission from S. Turner and P.R. Buseck, Science, 1981, 212, 1024. 1981 AAAS)...

The first ordered microporous transition metal oxides were microporous manganese oxides, known as octahedral molecular sieves (OMS). The manganese oxide OMS are classified into three families the pyrolusite-ramsdellite family with a (1 x n) channel structure the hollandite-romanechite family with a (2 x n) channel structure ... 

Figure 3.1 Structure and pore of manganese oxide octahedral molecular sieves (OMS) (a) todorokite (3x3) channel (b) romanechite (2x3) channel and (c) hollandite (2 x 2) channel...

Generally, there are two major structural forms for these minerals chain or tunnel structures, and layer structures. All of these forms are comprised of MnOs octahedras. Water molecules and/or other cations (8) are ofien present at various sites in the structures. Mn oxides having a chain or tunnel structure include pyrolusite, ramsdellite, hollandite, romanechite, and todorokite. Typical structures for the chain or tunnel type Mn oxide mineral are presented in Figure 1. Lithiophorite, chalcophanite, and bimessite are examples of Mn oxide minerals havii a layer structure. Typical structural maps are shown in Figure 2. 

Mn02 frameworks with even larger tuimels can be found in Nature, with two of the best-known examples being romanechite A2Mn50io x H20 (A=Ba, K, . .. tunnel size 2x3) and todorokite (tuimel size 3x3) [102, 103]. The detailed description of these materials is beyond the scope of this chapter. 

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