Elements and Performance Criteria

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:
sedimentary deposit
volcanic deposit (igneous)
erratic boulders
replacement cavities (nobbies, glauberite)
seams
volcanic and erosion sediments
opal replacing:
fossils
wood.
Sources of opal worldwide may include:
Australia
Brazil
Hawaii
Indonesia
Mexico
Slovakia
USA.
Locations of opal fields may include:
New South Wales - Lightning Ridge and White Cliffs
Queensland - various places including Winton, Quilpie, Jundah and Yowah
South Australia - Coober Pedy, Mintabie and Andamooka.
Base and background colours may include:
black
boulder - ironstone
dark
light.
Predominant colours and patterns may include:
colours, such as:
blue
green
orange
red
violet
yellow
patterns, such as:
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 and imperfections
pattern
play of colour
predominant colour
quality of cut (shape/proportions)
shape, size and weight
thickness of colour bar
type.
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.
Natural opal is classified as:
common opal and potch
precious opal.
Substances used to simulate opal and synthetic opal-like substances may include:
simulants - Gilson opal
synthetics - for example plastics and 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
any treatment other than cutting and polishing must be disclosed.

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.

Overview of assessment

Critical aspects for assessment and evidence required to demonstrate competency in this unit
Evidence of the ability to:
identify and describe the characteristics of the different types of opal using correct terminology and equipment
apply principles of valuation and determine the authenticity of opal materials.
Context of and specific resources for assessment
Assessment must ensure access to:
opals from various sources.
Method of assessment
A range of assessment methods should be used to assess practical skills and knowledge. The following examples are appropriate for this unit:
observation of processes and procedures
oral and/or written questioning on underpinning knowledge and skills
evaluation of the final product
review of portfolios of evidence
review of third-party workplace reports of on-the-job performance by candidate.
Assessment methods should closely reflect workplace demands (e.g. literacy) and the needs of particular groups (e.g. 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).
Guidance information for assessment
Holistic assessment with other units relevant to the industry sector workplace and job role is recommended.