File:Precious opal (Koroit Opal Field, Queensland, Australia) 2 (29237103553).jpg
Original file (2,700 × 2,492 pixels, file size: 3.95 MB, MIME type: image/jpeg)
Captions
Summary
[edit]DescriptionPrecious opal (Koroit Opal Field, Queensland, Australia) 2 (29237103553).jpg |
Precious opal ("boulder opal") from Australia. (public display, Denver Museum of Nature & Science, Denver, Colorado, USA) 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 specimen shown above is "boulder opal" from Queensland's Koroit Opal Field. The sample consists of a spider web-like network of precious opal veins within the host rock. Published research has shown that opalization occurred during Late Oligocene (see Senior et al., 1977) Stratigraphy: Winton Formation, Albian Stage to Cenomanian Stage, mid-Cretaceous Locality: unrecorded site in the Koroit Opal Field, southern Queensland, northwestern Australia Photo gallery of opal: <a href="http://www.mindat.org/gallery.php?min=3004" rel="nofollow">www.mindat.org/gallery.php?min=3004</a> References 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. Senior et al. (1977) - The geology and magnetic characteristics of precious opal deposits, southwest Queensland. Bureau of Mineral Resources, Journal of Australian Geology & Geophysics 2: 241-251. |
Date | |
Source | Precious opal (Koroit Opal Field, Queensland, Australia) 2 |
Author | James St. John |
Licensing
[edit]- You are free:
- to share – to copy, distribute and transmit the work
- to remix – to adapt the work
- Under the following conditions:
- attribution – You must give appropriate credit, provide a link to the license, and indicate if changes were made. You may do so in any reasonable manner, but not in any way that suggests the licensor endorses you or your use.
This image was originally posted to Flickr by James St. John at https://flickr.com/photos/47445767@N05/29237103553 (archive). It was reviewed on 30 November 2019 by FlickreviewR 2 and was confirmed to be licensed under the terms of the cc-by-2.0. |
30 November 2019
File history
Click on a date/time to view the file as it appeared at that time.
Date/Time | Thumbnail | Dimensions | User | Comment | |
---|---|---|---|---|---|
current | 16:51, 30 November 2019 | 2,700 × 2,492 (3.95 MB) | Ser Amantio di Nicolao (talk | contribs) | Transferred from Flickr via #flickr2commons |
You cannot overwrite this file.
File usage on Commons
There are no pages that use this file.
Metadata
This file contains additional information such as Exif metadata which may have been added by the digital camera, scanner, or software program used to create or digitize it. If the file has been modified from its original state, some details such as the timestamp may not fully reflect those of the original file. The timestamp is only as accurate as the clock in the camera, and it may be completely wrong.
Image title |
|
---|---|
Camera manufacturer | OLYMPUS IMAGING CORP. |
Camera model | TG-1 |
Exposure time | 1/50 sec (0.02) |
F-number | f/10 |
ISO speed rating | 200 |
Date and time of data generation | 11:35, 26 October 2013 |
Lens focal length | 10.29 mm |
Orientation | Normal |
Horizontal resolution | 314 dpi |
Vertical resolution | 314 dpi |
Software used | Adobe Photoshop CS2 Macintosh |
File change date and time | 19:20, 22 September 2016 |
Y and C positioning | Co-sited |
Exposure Program | Creative program (biased toward depth of field) |
Exif version | 2.3 |
Date and time of digitizing | 11:35, 26 October 2013 |
Meaning of each component |
|
APEX exposure bias | 0 |
Maximum land aperture | 2 APEX (f/2) |
Metering mode | Pattern |
Light source | Unknown |
Flash | Flash fired, auto mode |
Supported Flashpix version | 1 |
Color space | sRGB |
File source | Digital still camera |
Custom image processing | Normal process |
Exposure mode | Auto exposure |
White balance | Auto white balance |
Digital zoom ratio | 1 |
Focal length in 35 mm film | 57 mm |
Scene capture type | Standard |
Scene control | Low gain up |
Contrast | Normal |
Saturation | Normal |
Sharpness | Normal |
Receiver status | Measurement interoperability |
Reference for direction of image | Magnetic direction |
Direction of image | 58 |
GPS tag version | 0.0.3.2 |
Supported Flashpix version | 1 |
Image width | 2,700 px |
Image height | 2,492 px |
Date metadata was last modified | 15:20, 22 September 2016 |
IIM version | 2 |