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The range statement relates to the unit of competency as a whole. It allows for different work environments and situations that may affect performance. Bold italicised wording, if used in the performance criteria, is detailed below. Essential operating conditions that may be present with training and assessment (depending on the work situation needs of the candidate, accessibility of the item, and local industry and regional contexts) may also be included. |
Formation of opal may include: | opal combining with other mineralsopal formed in a sedimentary depositopal formed in a volcanic deposit (Igneous)opal formed in erratic bouldersopal formed in replacement cavities (nobbies, glauberite xls.)opal formed in seamsopal formed in volcanic and erosion sedimentsopal replacing fossilsopal replacing wood. |
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Sources of opal worldwide may include: | AustraliaBrazilHawaiiIndonesiaMexicoSlovakiaUSA. |
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Locations of opal fields in Australia may include: | New South Wales - Lightning Ridge, White CliffsQueensland - various places including Winton, Quilpie, Jundah, YowahSouth Australia - Coober Pedy, Mintabie, Andamooka. |
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Base and background colours may include: | blackboulder - ironstonedarklight. |
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Predominant colours and patterns may include: | colours such as but not limited to:bluegreenorangeredvioletyellow |
| patterns such as but not limited to:broadChinese writingflagstoneharlequinpeacock tailpin firerolling flashsheenstraw. |
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Other factors that influence an opal's value may include: | availability of supplyeconomic climatemining restrictionsoriginpolitical situationrarityweightwhether the sale is wholesale or retail. |
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Principles of valuing may include: | body colourbrillianceinclusion/imperfectionspatternplay of colourpredominant colourquality of cut (shape/proportions)shapesize/weightthickness of colour bartype. |
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The gemmological characteristics may include: | chemical compositioncolourfracturehardnessphosphorescencerefractive indexspecific gravity. |
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Gemmological instruments may include: | microscoperefractometerS.G. scalesstandard 10X loupeultraviolet lampsalso the naked eye gives a good judgment. |
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Natural opal is classified as: | common opal and potch - opal which does not exhibit a play of colourprecious opal - exhibiting a play of colour. |
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Substances used to simulate opal and synthetic opal-like substances may include: | simulants - Gilson opalsynthetics - for example plastics; slocum stone. |
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Opals of various types may include: | composite natural opal - doublets; triplets; mosaic and chip opalsnatural opal type 1 (opal in one piece in its natural state apart from cutting and polishing)natural opal type 2 - opal naturally attached to the host rock - boulder opalnatural opal type 3 - opal intimately diffused as infilling in pores or between the grains of the host rock - matrix opalvarieties of opal: (N1 to N9 represents gradation from black to white in approximately 10% intervals)black - opal which shows a play of colour within or on a black or very dark body tone (N1,N2, N3, N4)dark - opal which shows a play of colour within or on a dark body tone (N5, N6)light - opal which shows a play of colour within or on a light body tone (N7, N8, N9). |
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Opal treatments may include: | treatments applied to improve appearance, structure or durabilityNote: Any treatment other than cutting and polishing must be disclosed. |
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