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Elements and Performance Criteria

  1. Develop knowledge of opal geology.
  2. Apply the principles of grading and quality assessment to opal.
  3. base and background colours
  4. the predominant colours and patterns
  5. other factors that influence an opal's value.
  6. Distinguish natural opal from man-made varieties.
  7. Identify and describe the different types of opal using correct opal nomenclature and terminology.

Evidence Required

The evidence guide provides advice on assessment and must be read in conjunction with the performance criteria required skills and knowledge range statement and the Assessment Guidelines for the Training Package

Critical aspects for assessment and evidence required to demonstrate competency in this unit

Assessment must confirm accurate identification and description of the characteristics of the different types of opal using correct terminology and equipment in a variety of work environments and the ability to apply principles of valuation and determine the authenticity of opal materials

Context of and specific resources for assessment

This unit may be assessed in a work environment in a simulated work environment or in a combination of these situations

Method of assessment

For valid and reliable assessment of this unit evidence should be gathered through a range of methods to indicate consistent performance

Assessment of this unit of competence will usually include observation of processes and procedures oral andor written questioning on underpinning knowledge and skills and other methods as required

Assessment methods should closely reflect workplace demands eg literacy and the needs of particular groups eg people with disabilities and people who may have literacy or numeracy difficulties such as speakers of languages other than English remote communities and those with interrupted schooling

Competence in this unit must be assessed over a period of time in order to ensure consistency of performance over the range of variables and contexts applicable to the work environment


Range Statement

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 minerals

opal formed in a sedimentary deposit

opal formed in a volcanic deposit (Igneous)

opal formed in erratic boulders

opal formed in replacement cavities (nobbies, glauberite xls.)

opal formed in seams

opal formed in volcanic and erosion sediments

opal replacing fossils

opal replacing wood.

Sources of opal worldwide may include:

Australia

Brazil

Hawaii

Indonesia

Mexico

Slovakia

USA.

Locations of opal fields in Australia may include:

New South Wales - Lightning Ridge, White Cliffs

Queensland - various places including Winton, Quilpie, Jundah, Yowah

South Australia - Coober Pedy, Mintabie, Andamooka.

Base and background colours may include:

black

boulder - ironstone

dark

light.

Predominant colours and patterns may include:

colours such as but not limited to:

blue

green

orange

red

violet

yellow

patterns such as but not limited to:

broad

Chinese writing

flagstone

harlequin

peacock tail

pin fire

rolling flash

sheen

straw.

Other factors that influence an opal's value may include:

availability of supply

economic climate

mining restrictions

origin

political situation

rarity

weight

whether the sale is wholesale or retail.

Principles of valuing may include:

body colour

brilliance

inclusion/imperfections

pattern

play of colour

predominant colour

quality of cut (shape/proportions)

shape

size/weight

thickness of colour bar

type.

The gemmological characteristics may include:

chemical composition

colour

fracture

hardness

phosphorescence

refractive index

specific gravity.

Gemmological instruments may include:

microscope

refractometer

S.G. scales

standard 10X loupe

ultraviolet lamps

also the naked eye gives a good judgment.

Natural opal is classified as:

common opal and potch - opal which does not exhibit a play of colour

precious opal - exhibiting a play of colour.

Substances used to simulate opal and synthetic opal-like substances may include:

simulants - Gilson opal

synthetics - for example plastics; slocum stone.

Opals of various types may include:

composite natural opal - doublets; triplets; mosaic and chip opals

natural 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 opal

natural opal type 3 - opal intimately diffused as infilling in pores or between the grains of the host rock - matrix opal

varieties 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).

Opal treatments may include:

treatments applied to improve appearance, structure or durability

Note: Any treatment other than cutting and polishing must be disclosed.