File:Black opal (Stayish Mine, Wollo Province, Ethiopia) 8 (23227454253).jpg
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摘要
描述Black opal (Stayish Mine, Wollo Province, Ethiopia) 8 (23227454253).jpg |
Precious opal (black opal) from the Tertiary of Ethiopia. (cut & faceted specimen; the long axis is 8 to 9 mm) A mineral is a naturally-occurring, solid, inorganic, crystalline substance having a fairly definite chemical composition and having fairly definite physical properties. At its simplest, a mineral is a naturally-occurring solid chemical. Currently, there are over 4900 named and described minerals - about 200 of them are common and about 20 of them are very common. Mineral classification is based on anion chemistry. Major categories of minerals are: elements, sulfides, oxides, halides, carbonates, sulfates, phosphates, and silicates. The silicates are the most abundant and chemically complex group of minerals. All silicates have silica as the basis for their chemistry. "Silica" refers to SiO2 chemistry. The fundamental molecular unit of silica is one small silicon atom surrounded by four large oxygen atoms in the shape of a triangular pyramid - this is the silica tetrahedron - SiO4. Each oxygen atom is shared by two silicon atoms, so only half of the four oxygens "belong" to each silicon. The resulting formula for silica is thus SiO2, not SiO4. Opal is hydrous silica (SiO2·nH2O). Technically, opal is not a mineral because it lacks a crystalline structure. Opal is supposed to be called a mineraloid. Opal is made up of extremely tiny spheres (colloids - <a href="https://www.uwgb.edu/dutchs/acstalks/acscolor/OPALSPHR.jpg" rel="nofollow">www.uwgb.edu/dutchs/acstalks/acscolor/OPALSPHR.jpg</a>) that can be seen with a scanning electron microscope (SEM). Gem-quality opal, or precious opal, has a wonderful rainbow play of colors (opalescence). This play of color is the result of light being diffracted by planes of voids between large areas of regularly packed, same-sized opal colloids. Different opalescent colors are produced by colloids of differing sizes. If individual colloids are larger than 140 x 10-6 mm in size, purple & blue & green colors are produced. Once colloids get as large as about 240 x 10-6 mm, red color is seen (Carr et al., 1979). Not all opals have the famous play of colors, however. Common opal has a wax-like luster & is often milky whitish with no visible color play at all. Opal is moderately hard (H = 5 to 6), has a white streak, and has conchoidal fracture. Several groups of organisms make skeletons of opaline silica, for example hexactinellid sponges, diatoms, radiolarians, silicoflagellates, and ebridians. Some organisms incorporate opal into their tissues, for example horsetails/scouring rushes and sawgrass. Sometimes, fossils are preserved in opal or precious opal. The gorgeous black opal shown above is from a relatively newly discovered deposit in northern Ethiopia. A widespread nodule horizon of black precious opal occurs at the boundary between a lithified volcanic ash unit and a clay bed. The opal nodules are hosted in clay. For more info., see: <a href="http://www.gia.edu/gems-gemology/winter-2014-gemnews-new-deposit-black-opal-from-ethiopia" rel="nofollow">www.gia.edu/gems-gemology/winter-2014-gemnews-new-deposit...</a> Locality: Stayish Mine, near the town of Gashena, Wollo Province, northern Ethiopia, eastern Africa Photo gallery of opal: <a href="http://www.mindat.org/gallery.php?min=3004" rel="nofollow">www.mindat.org/gallery.php?min=3004</a> Reference cited: Carr et al. (1979) - Andamooka opal fields: the geology of the precious stones field and the results of the subsidised mining program. Geological Survey of South Australia Department of Mines and Energy Report of Investigations 51. 68 pp. |
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來源 | Black opal (Stayish Mine, Wollo Province, Ethiopia) 8 |
作者 | James St. John |
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這幅圖片原始出處為Flickr的https://flickr.com/photos/47445767@N05/23227454253 ,作者為James St. John 。經機器人FlickreviewR 2在2019年11月30日審查後確定為採用cc-by-2.0的協議授權使用。 |
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目前 | 2019年11月30日 (六) 16:49 | 1,115 × 578(278 KB) | Ser Amantio di Nicolao | Transferred from Flickr via #flickr2commons |
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相機製造商 | Canon |
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相機型號 | Canon PowerShot D10 |
曝光時間 | 1/60 秒 (0.016666666666667) |
光圈值 | f/9 |
ISO 速率 | 80 |
資料產生的日期時間 | 2015年12月8日 (二) 18:43 |
焦距 | 7.23毫米 |
影像標題 | |
寬度 | 4,000 px |
高度 | 3,000 px |
每像素位元 |
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像素合成 | RGB |
方位 | 標準 |
像素數量 | 3 |
水平解析度 | 180 dpi |
垂直解析度 | 180 dpi |
使用軟體 | Adobe Photoshop Elements 13.0 (Macintosh) |
檔案修改日期時間 | 2015年12月19日 (六) 15:41 |
亮度與彩度位置 | 同時取樣 |
Exif 版本 | 2.21 |
數位化的日期時間 | 2015年12月8日 (二) 18:43 |
每像素內含 |
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影像壓縮模式 | 3 |
APEX 快門速度 | 5.90625 |
APEX 光圈 | 6.34375 |
APEX 曝光補償 | −1 |
最大陸地光圈 | 3.34375 APEX(f/3.19) |
測光模式 | 模式 |
閃光燈 | 閃光燈已開啟、強制閃光燈開啟、防紅眼模式 |
支援的 Flashpix 版本 | 1 |
色彩空間 | sRGB |
X 軸焦平面解析度 | 16,460.905349794 |
Y 軸焦平面解析度 | 16,483.516483516 |
焦平面解析度單位 | 英寸 |
感光模式 | 單晶片彩色區域感測器 |
檔案來源 | 數位相機 |
自訂影像處理 | 一般程序 |
曝光模式 | 手動曝光 |
白平衡 | 自動白平衡 |
數位變焦比率 | 1 |
場景拍攝類型 | 人像 |
使用鏡頭 | 6.2-18.6 mm |
詮釋資料最後修改日期 | 2015年12月19日 (六) 08:41 |
原始文件唯一識別碼 | C94C98FC438DE046B088C03D2C0A13E4 |