Realgar, As

Each of these elements occurs naturally as a sulphide ore arsenic as realgar As S,, orpiment As, Sg and arsenical pyrites with approximate formula FeAsS antimony as stibnite Sb2S3 and bismuth as B12S3. 

The crystalline structure of realgar consists of rings of AS4S4 (Klein, 2002, 363). That is, arsenic occurs as As(II) in realgar, as well as amorphous AsS. However, As(II) is not stable in aqueous solutions. Instead, As(II) oxidizes to As(III) in the compounds before being released into solution (Lengke and Tempel, 2005, 350). 

Cotter Powder. An expl mixt consisting of KClO, 50 realgar (As S ) 50 5... 

Fig.52.1 shows the burning fuse of a shell. Some years ago such a fuse fell on a straw-thatched house and caused a fire. Fig.52.2 shows an ignition device for a smoke in which a fuse is burning. The cinder accumulates at the outlet of the fuse, and is intermittently blown out through small holes as small drops which can drop on the composition to cause an unexpected ignition. To avoid these phenomena we must improve the composition so that it will not produce the fire ball material. For this purpose the sulphur content should be decreased, as we see in Fig. 9. It is also better not to use realgar as the component, because it helps the production of the fire...

The boric acid prevents the potassium nitrate and aluminium from reacting v ith each other(R.Lancaster Fireworks, p.31(1972)). No.l and No.2 produce a pretty golden fire dust. No.3 produces a somewhat reddish gold effect, and looks more elegant than Nol and No.2. When we use antimony trisulphide, sulphur and realgar, as components in one composition with various ratios between them, various colour tones of gold can be obtained. 

With AS4S4 there are two possible geometrieal isomers of the moleeule depending on whether the 2 As-As bonds are skew or adjaeent, as shown in Fig. 13.17. Realgar (mp307°) adopts the more symmetrie D2d form with skew As-As... 

FIGURE 15.3 The minerals (from left to right) orpiment, As2S, stibnite, Sb,S, and realgar, As4S4 are all ores that have been used as sources of Group 15A elements. 

Orpiment is As,5, and realgar is As4S4. Orpiment is yellow and realgar is orange-red. They are both used as... 

In realgar the short non-bonding contact distances are 3.3 A for sulfur-sulfur, 3.6 A for sulfur-arsenic, and 3.5 A for arsenic-arsenic. They are accordingly about 1.2 A greater than the corresponding single-bond lengths, as found in other crystals. 

The difference in mineralogy of the Kuroko and present-day back-arc deposits are (1) metastable phases such as native sulfur, wurtzite, and amorphous silica are poor in the Kuroko deposits (2) arsenic minerals such as jordanite, tetrahedrite-tennantite, native arsenic, and realgar are common in the present day back-arc deposits (Okinawa Myojinsho Knoll Caldera), but rare in Kuroko deposits except tetrahedrite-tennantite (3) secondary minerals such as cerussite and covellite are common in present day back-arc deposits (e.g., Okinawa, Myojinsho Knoll Caldera) (4) Dendritic texture is common in the present day back-arc deposits. 

Although mineralogy is different in different site, the more abundant minerals in back-arc deposits than in midoceanic ridge deposits are barite, anhydrite, electrum, As-minerals (realgar, orpiment), tetrahedrite-tennantite and galena. 

An experimental study at 350°C on the interaction between NaCl solution and graywacke which occurs widely in island arc geologic setting indicates that the final solution contains (0.6-0.7) ppm As (Bischoff et al., 1981). Analytical data on As concentration of hydrothermal solution at back-arc basins are few. Arsenic concentration of hydrothermal solution at Lau Basin is 6.0-8.2 ppm (Foquet et al., 1991). We can also estimate As concentration of hydrothermal solution based on the solubility data on orpiment and realgar because these As-bearing minerals are common in back-arc basin deposits (e.g., Okinawa Trough, Kuroko deposits). 

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