Opal Classification Reference Tables

These are the technical scales used to describe every opal in the Christianos Opals inventory. Each item is classified by type, body tone, profile (dome), brightness, shape and mining origin. The same scales are widely used across the Australian opal trade.

Opal Type

The broad category of the opal as a gem material.

Code	Type	Definition
1	SOLID OPAL	NATURAL HOMOGENEOUS ("SOLID") OPAL
2	BOULDER OPAL	NATURAL OPAL ATTACHED TO HOST ROCK ("SOLID BOULDER")
3	BOULDER MATRIX	NATURAL OPAL IN HOST ROCK ("BOULDER MATRIX")

Body Tone (N1–N9)

The underlying darkness of the opal, judged independent of the play-of-colour. N1 is jet black, N9 is white. Three families: Black (N1–N4), Dark (N5–N6), Light (N7–N9). For a deep guide including how body tone is judged and how it affects value, see Opal Body Tone Explained (N1–N9).

Code	Description	Family
N1	BLACK	Black
N2	BLACK	Black
N3	BLACK	Black
N4	BLACK	Black
N5	DARK	Dark
N6	DARK	Dark
N7	LIGHT	Light
N8	LIGHT	Light
N9	LIGHT	Light

Profile (Dome)

The cross-sectional profile of the cut stone — how high the dome rises above the girdle. Affects how light is gathered into the play-of-colour and how the stone sits in a jewellery setting.

Icon	Code	Profile
	1	Flat Top
	2	Low Dome
	3	Medium Dome
	4	High Dome
	5	Undulating
	6	Carved Flattish
	7	Carved Bulky
	8	Faceted
	9	Faceted Fancy
	10	Roughed Finish
	11	Tablet
	12	Concave
	13	Cleaned in Natural State
	14	Carving
	15	Slightly Concave

Brightness (Fire Intensity)

How vivid and intense the play-of-colour is when the stone is viewed in good light. Graded 1–10. Brightness is often the single most important factor in the value of any opal, regardless of body tone.

Code	Level	Definition
1	1 No Visible Fire	Common Opal or Potch
2	2 Pale Fire	Pale Fire
3	3 Subdued Fire	Subdued Fire
4	4 Moderate Fire Intensity	Moderately Bright Fire
5	5 Average Fire Intensity	Average Fire Intensity
6	6 Lively Fire Intensity	Lively Fire Intensity
7	7 Bright Fire	Bright Fire
8	8 Very Bright Fire	Very Bright Fire
9	9 Extremely Bright Fire	Extremely Bright Fire
10	10 Exceptionally Bright Fire	Exceptionally Bright Fire

Shape

The cut shape of the finished stone. We use a short label code on stock labels.

Code	Shape	Label	Common name
1	Oval	OVL	Oval
2	Long Oval	OVE	Long Oval
3	Circular	RND	Round
4	Drop Shape	DRP	Drop or Pear Shape
5	Long Drop	DRE	Long Drop
6	Square	SQR	Square
7	Rectangular	REC	Rectangular
8	Free Shape	FRF	Freeform
9	Strip	STR	Strips
10	Marquis	MRQ	Marquis
11	Heart	HRT	HEART
12	Cushion Cabochon	CUS	CUSHION [TRIANGLE] - CABOCHON
13	Triangular Cabochon
14	Kite	KITE	Kite Shape
15	Various	MULT	Various Shapes
16	Other	OTR	Other Shape

Mining Origin

The opal field or sub-field where the stone was mined. Major Australian fields are Lightning Ridge (NSW), Coober Pedy, Mintabie, Lambina and Andamooka (SA), and the Queensland boulder fields (Quilpie, Yowah, Koroit, Winton). See our guides on Lightning Ridge and Coober Pedy for background.

Code	Mining Origin
1	COOBER PEDY
2	LIGHTNING RIDGE
3	QUEENSLAND
4	ANDAMOOKA
5	MINTABIE
6	LAMBINA
7	SOUTH AUSTRALIA
8	UNKNOWN
10	COOBER PEDY (EIGHT MILE DIGGINGS)
11	COOBER PEDY (SHELL PATCH DIGGINGS)
12	COOBER PEDY (OLYMPIC DIGGINGS)
13	COOBER PEDY (TEN MILE DIGGINGS)
20	LIGHTNING RIDGE - TOWN SURROUNDS
21	LIGHTNING RIDGE - COOCORAN
22	MULGA RUSH
23	GRAWIN
24	LIGHTNING RIDGE - CARTERS RUSH
25	LIGHTNING RIDGE - JAGG HILL
26	LIGHTNING RIDGE - MOONSHINE
27	LIGHTNING RIDGE - WYOMING
29	WHITE CLIFFS NSW
30	KOROIT, QLD
31	WINTON AREA, QLD