Opal Research


The following references summarise research and technical papers over the past 40 years. The list was originally prepared by the Editor of the Australian Gemmologist, Grahame Brown, with subsequent updating since 2000 by Anthony Smallwood. Back issues of the Australian Gemmologist can be purchased from their website at www.austgem.gil.com.au .
This page is divided in to the following Sections. Click to go directly to each:

1. Opal Papers in the Australian Gemmologist

2. Other References

2.1 Classification and evaluation of opal
2.1 Synthetic opal
2.3 Synthetic imitation opal
2.4 Natural imitation opal
2.5 Treated opal

3. Scientific References

4. References to opal in other mineral papers



Extracted from the original Australian Gemmologist summary of articles: Australian Gemmologist April - June 2000 Volume 20 Number 10 p416, G Brown Editor.

updates by Anthony Smallwood, 2000-2005





August, 1958


Andamooka field excursion

R. Harvey

December 1958


New discovery in Western Australia

P. McN

May 1959


Some notes on a recent West Australian mineral discovery

D.R. Walter

May 1959


Birth of the opal


July 1959


The Japanese opal market

R.B. Stokes

May 1960




Black opal

L. Hudson


Opal deposits and the Hayricks opal mine, Quilpie

H.G.S. Cribb

July 1960


The noble opal of Australia

A.A. Wirth

Nov-Dec 1960


Opal in the Eulo District

R.R. Dowding

December 1961


Gemstones of Australia


March 1962


The opal market

J.D. Altmann

June 1962


Microstructures in opal potch from Andamooka


February 1963


Research on opal

F. Lechman

July 1963


Hungarian opal


January 1964


An unusual colour pattern in precious opal from Andamooka

P.A. Males

February 1964



Relics from the past

F. Dowding


The miners of Koroit (poem)

R. Doeding

September 1964


Jasper-opal associated with diatomite from Cooma, NSW

P.A. Males

November 1964


Quartz matrix opal

P.Darragh & Gaskin

January 1965


The opal: Gem of mystery


February 1965


Matrix opal, Andamooka, South Australia

P.A. Males

April, 1965


The origin of colour in opal

P.J. Darragh &

J.V. Sanders

May 1965


Synthetic opals search

The Sun Herald

June 1965


The geology of Australian gemstone deposits

J.C. Liddy

January 1966


The geological environment of Australian opal

P.A. Males

March 1966


Boulders of opal

L.G. Cram

May 1966


A living opal

M.F. Day

June 1966


Restrictions on buying opal

A. H. Stevenson (Editor)

October 1966


Opal pseudomorphs and the candle-box trade

F.E. Murphy (Chapter from: They struck opal)

December 1966




The nature and origin of opal

P.J. Darragh, A.J. Gaskin  & J.V. Sanders


Go to Andamooka

G. Woods

January 1967



Iris opal from Mexico

J. Sinkankas


Opalised ‘steel band’ from Lightning Ridge

P.A. Males

June 1967


Opal geology

J.H. Oughton

November 1967


Phosphorescence in Australian opal

P.A. Males

February 1968


Precious opal in an unusual environment

P.A. Males

August 1968


Mexican fire opal

P.A. Males

November 1968


Opal in volcanic rock

P.A. Males

May 1969


A new occurrence of precious opal of volcanic origin near Mullimbimby, New South Wales

R.O. Chalmers


The first discovery of Australian opal

N. Clayton

November 1969


Volcanic gem opals: The results of an examination by electron microscopy

P.J. Darragh &

J.V. Sanders

February 1970


Opal story

W. Gower

May 1970


Opal in the nickel search in Western  Australia

R.T. Prider

May 1971






The classification of black opal

NSW Opal Research Group


Some thoughts on opal

Editorial Committee


Definition of black opal

Altman & Cherny


Myth of the Geierstein opal

P.B. Lapworth

August 1971


A scanning microscope study of the morphology of opal

E.R. Segnit,

C.A. Anderson &

J.B. Jones

November 1971



Black opal nomenclature

A. Kalokerinos


Spotted matrix opal

P.A. Males

February 1972


Opal nomenclature discussion

P.A. Males

August 1972


Lightning Ridge nobbies’ and the ‘Chainman’s hat’

P.A. Males

February 1973


Inclusions in opal

P.A. Males

August 1973




Precious opal – Developments towards synthesis

P.J. Darragh &

J.L. Perdrix


Opal classification – Your problem

J.H. Oughton (Editor)

November 1973


Scanning electron microscopy and opals

R.A. Ball & A.S. Malin

May 1974


Brazilian precious opal

P.A. Males

February 1975




Classification and nomenclature of precious opal

N.A. Clayton


Precious opal in Queensland

B.R. Senior

May 1975


Opal from Coolgardie, Western Australia

R.A. Ball


Notes on identification of Gilson synthetic opal

G.A. Tombs


Opal references & abstracts

R.A. Ball & N. Clayton

August 1975


Chinaman’s hats

K.A. Sheens


New synthetic gems set a problem

J.H. Oughton

November 1975


On the origin of volcanic opal from Houhlahan’s creek (near Teven)

I.A. Mumme,

L. Seibright & R. Ball

August 1976


Indonesian opal

B. O’Leary &

R.A. Ball

November 1976


Opal in Western Queensland

R.A. Ball & A. Daniels

February 1977



Black opal

B. O’Leary

November 1977


Natural or synthetic?

R.A. Ball


Synthetic opals

P.J. Darragh,

A.J. Gaskin &

 J.V. Sanders

February 1978





Identification of synthetic opal - A review

R.A. Ball


Slocum stone

P.J. Darragh &

J.V. Sanders


Imitation opal

R.A. Ball

November 1978



Recognition of synthetic opal

N.P. Jamieson

February 1979



Porous Gilson synthetic black opal

A.D.C. Robertson


Opal references & abstracts – Part 2

R.A. Ball & N. Clayton

May 1979


Opal references & abstracts – Part 2

R.A. Ball & N. Clayton

August 1979



Treated Brazilian opal

G. Brown & J. Snow


Opals from the air



Opal references & abstracts – Part 2

R.A. Ball & N. Clayton

November 1979



Suggestions for nomenclature of opals

J.D. Altmann


Synthetic opal for natural opal

R.A. Ball

May 1980


The opal: Gem of mystery


August 1981


Jelly opal from White Cliffs

J.V. Sanders

February 1982


New synthetic opal made of plastics

N. Horiuchi

August 1982


Common opal and potch opal

R.A. Ball

November 1982



Honey opal

R.A. Ball


More synthetic opal

G.A. Tombs &

W.J. Joris

February 1983


Precious opal from new Zealand

R.a. Ball

August 1983



Certification of opal

G. Sherman


A proposal for classification of opals

J.V. Sanders

November 1983


Crystal opal (Letter to the Editor)

J.V. Sanders

May 1984


Crystal opal (Letter to the Editor)

J.S. Taylor


Opal pineapple (Mineralien Magazin)

S.M. review

February 1985



Black opal: A brief review

R.A. Ball


Opal pineapple (Letter to the Editor)

R.O. Chalmers

November 1985


Role of water in cracking of opal

G. Pearson

May 1986


Opals from Mexico

E. Gubelin

August 1986


The Australian opal fields

E. Sherman

November 1986




Opal pineapples from White Cliffs

G. Pearson


Boulder opal triplet imitating natural solid boulder opal

R. Brightman &

D. Sandeman

February 1987


More on crystal opal

B. O’Leary

May 1987


A system for evaluation of opal

S. Haugen


On the structure of sedimentary opal


August 1987



Australian triplet opals (Letter to the Editor)

L, Cram &

J.V. Sanders


Crystal opal and catamites (Letter to the Editor)

F.H. Thrupp


Pronounced flow structure in opal

J. Koivula


Japanese synthetic jelly opal

G. Brown & J. Snow

November 1987




Unusual opal triplet

G. Brown & J. Snow


LWUV fluorescence of gemstones; A photographic review

J. Snow & G. Brown

February 1988


Precious opal and the weathered profile at Coober Pedy

R.S. Robertson &

D.C. Scott

November 1988


Impregnated opal

G. Brown & J. Snow

February 1989


Black-dyed synthetic opal

G. Brown &

P. Callaway

May 1989


Siliciophite: Australian cat’s-eye opal

G. Brown


Unusual opals

G. Brown, J. Snow & H. Bracewell

August 1989


A gemmological study of ‘Opalite’ and ‘Opal Essence’

J. Koivula & R. Kammerling


Yundamindera fire opal

G. Brown &

H. Bracewell

November 1989


An investigation of three imitation opalised shells

J. Koivula &

R Kammerling


Imitation opalised shells (Letter to the Editor)

M. Benjamin

August 1990


Scenic Peruvian opal

G. Brown et al.

November 1990



Imitation opalised shells (A reply)

J. Koivula &

R. Kammerling

February 1991






Examination of a plastic coated ‘sugar treated’ opal

R. Kammerling &

J. Koivula

384, 382

Significant Australian opals


May 1991



Carved opal doublet

G. Brown, S, Kelly & H. Bracewell


Black pained opal

G. Brown, S, Kelly & H. Bracewell

November 1991


Plastic imitation opals purchased in Thailand

R. Kammerling,

J. Koivula & E. Fritsch

February 1992




The Mintabie opal field.

I.J. Townsend


Cause of colour in opal (Letter to the Editor)

G. Brown


Novel assembled opals from Mexico

R. Kammerling &

J. Koivula

May 1992


Robotic opal cutting

A. Cody & G. Brown

February 1993




An historical note on the colour phenomenon in precious opal.

D. Hoover


A composite imitation of crystal opal

R. Kammerling &

J. Koivula

May 1993


Leopardwood mosaic opal

M. Sawicki &

G. Brown

August 1993


Eric saved


November 1993



Some far northern opal diggings in South Australia

G. Brown, J. Townsend & K. Endor

August 1994


A brief report on Indonesian opal

C. Lambert &

G. Brown

November 1994


Opal – Australia’s National Gemstone

A. Bartram

2nd Quarter 1995

64, 61

Grawin Rainbow

B. Parker

Jubilee issue 1995


Gemstones of NSW

R. Coenraads


Gemstones of Queensland

A.F. Wilson


Gemstones of South Australia

I.J. Townsend

1st Quarter 1996


Dyed opalised sandstone and conglomerate: A new gem product from Andamooka

J. Keeling &

I.J. Townsend

3rd Quarter 1996


The true story of white Cliffs

G. Rowe


Ethiopia: A new source for precious opal

D. Hoover,

T. Yohannes &

D. Collins

4th Quarter 1997


A new era for opal nomenclature

A. Smallwood

2nd Quarter 1998



An occurrence of microcrystalline opal, Nipple mountain, Kelowna, British Columbia, Canada

R. Coenraads &

R. Pogson

3rd Quarter 1998


An ?Australian synthetic opal

G. Brown

1st Quarter 1999


New opal cutting factory at Khao Yai, Thailand

R. Coenraads &

P. Elmer

2nd Quarter 1999




French opal

G. Brown


White Cliffs: Australia’s first commercial opal field - A century of history

G. Rowe

4th Quarter 1999


Statement respecting the opal industry at White Cliffs

T.C. Wollaston

1st Quarter 2000


A preliminary investigation of precious opal by laser Raman spectroscopy

A. Smallwood

2nd Quarter 2000


Papers on opal previously published in The Australian Gemmologist


3rd Quarter 2000


Present Russian synthetic and enhanced gemstones

V. Balitsky


Diffraction colours of opal: First spectrophotometric data

M. Ostrooumov & H.A. Talay

4th Quarter 2000


Australia’s gemstone resources and their markets

G. Brown

1st Quarter, 2001


The geology of Australian opal deposits

J. Townsend


A new theory for the genesis of opal

J.H. Behr, K. Behr, J.J. Watkins

2nd Quarter 2002


The Springsure deposit of Precious opal.

Roy Beattie

2nd Quarter 2002


Mexican gem opals: Nano and microstructures, origin of colour, comparison with other common opals of gemmological significance

E. Fritsch , Ostrooumov, A, Barreau, D. Albertini, A.-M. Marie, B. Lasnier, J. Wery


Interesting American opals: Wood replacement

I.J. Koivula & M. Tannous


Louisiana opal

G. Brown

3rd Quarter 2002


Classification of natural opal; type 1

J. Schellnegger


Some aspects of precious opal synthesis

S.V. Filin, A.I. Puzynin, V.V. Samoilov

4th Quarter 2002


Update on Australia’s gemstone & pearl resources

G. Brown


Australian sedimentary opal: Why is Australia unique?

D. Horton

3rd Quarter 2003


Notes on identification of Gilson Synthetic opal – Reprinted V12(6)

G. A. Tombs



35 years on a new look at Synthetic opal

A. G. Smallwood


2nd Quarter 2004


The Origin of Precious opal – A New Model

Byron Deveson

1st Quarter 2005


Papers pf Gemmological Interest- Precious volcanic opal from the Raduznoe deposit Russia,.photo and authors only

IAGOD – Conference

V.B Tishkina ,

M.I Lapina

2nd Quarter 2005


Opals from Java

H. Sujatmiko, H.C Einfalt, U. Henn

2.  Other Opal References – By subject.
2.1 Evaluation
Schellnegger, J. (2002) Classification of natural opal type 1. Australian Gemmologist, 21, Number 7, 269-277.
Smallwood, AG (2003) Evaluation of carved Lightning Ridge Black Opal. The NCJV Valuer, 21, Number 2, 2-7.
Cody A. Australian Precious Opal, A Guide Book for Professionals, 1991, 17, 41.
Downing PB - Opal identification and Value, Majestic Press 1992.
Evans PR - Opal, The Professional Valuation and Classification Guide.
Cram Len – Various.
Aracic Stephen – Discover opals .
2.2 Synthetic opals
Smallwood, AG. (2003) 35 years on A New look at Synthetic Opal. Australian Gemmologist, 21, Number 11,
Schmetzer K, An Investigation of the Synthetic Products of Gilson Showing a Play of colours, Journal of Gemmology Vol:19, No1, January 1984, p27.
Gunawardene M, Mertens R. - Gilson Created Fire Opal Imitation with Play if Colours - Journal of Gemmology Vol:19, No1, January 1984, p43.
Darragh PJ, Perdrix, JL, Notes on Synthetic Precious Opal. Journal of Gemmology, Vol 14, p215.
Darragh PJ, Perdrix, JL, Synthetic Opals, Australian Gemmologist, Volume 13, No4.
2.3 Synthetic Imitation opals
Burch CR, A Re-examination of Slocum Stone - with particular emphasis on inclusions. - Journal of Gemmology Vol:19, No.7, July 1985, p586.
Scarratt K, Kammerling RC, Koivula JI, Opalite Triplets - new imitations of opal. Journal of Gemmology Vol 23, No.8, 1993.
Horiuchi N, New Synthetic Opal Made of Plastics, Australian Gemmologist, February 1982, p213.
Ball RA, Imitation Opal, Australian Gemmologist, February 1978, p156.
Campbell ICC, Klienstubber A, Thomas AE, Some Comparisons between natural, gilson, inamori and simulated opals. South African Gemmologist, February 1987, p3.
Darragh PJ, Sanders JV, Slocum Stone. Australian Gemmologist, Volume 13, No.5, February 1978, p146.
2.4 Natural Imitation Opal
Weldon R, Ammolite: The colourful fossil gem - Jewellers Circular Keystone, June 1992, p46.
Sweaney, JL, Fire Agates of Deer Creek, Gems and Gemology, Spring 1979, p130.
2.5 Treated opals
Mitchell K, Oiled opals, Journal of Gemmology Vol:18, No.4, 1982, p339.
Brown, G. Treated Andamooka Matrix Opal, Gems and Gemology. Vol 27 (2), p100.
Keeling, J.L. Townsend, I.J, Dyed Opalised sandstone and conglomerate, Australian Gemmologist, Volume 19,No.5, p226.
3 Scientific References
ALONSO, P.J., HALLIBURTON, L.E., KOHNKE, E.E. & BOSSOLI, R.B., 1983. X-ray induced luminescence in crystalline SiO2. Journal of Applied Physics 54/9, 5369-5375.
ARACIC, S., 1996. Discover opals before and beyond 2000, with surface indications. Digital Press Company, Brisbane. Australia (limited edition).
AUSTIN, G.T., (1991). Gemstone production in Arizona, Colorado, Idaho, Montana, North Carolina, Oregon, Maine, Utah, Nevada and Tennessee. Mineral Industry Surveys, Bureau of Mines, US Department of the Interior, 13.
Australian Government Gazette, 1993. No. S229.
BALL, R.A., 1983. The structure of opal and opal simulants. University of New South Wales, Msc Thesis, Sydney, NSW, 85pp. (unpublished).
BALL, R.A., 1986. The structure of some opals and opal simulants, Gemmological Association of Australia, Sydney, NSW, Research Diploma, 43pp. (unpublished).
BALL, S.H., 1950. A Roman Book on Precious Stones. Lorrin L. Morrison and the Gemmological Institute of America, Los Angeles.
BARNES, L.C., TOWNSEND, I.J., ROBERTSON, R.S. & SCOTT, D.C., 1992. Opal, South Australia’s Gemstone. South Australian Department of Mines and Energy Handbook Number 5. Revised edition 1992.
BARTOLI, F., BITTENCOURT, ROSA D., DIORISSE M., MEYER, R., PHILLIPPY, R. & SAMAMA, J., 1990. Role of aluminium in the structure of Brazilian opals. European Journal of Mineralogy 2, 611-619.
BAUER, H.L. & STAAZ, M.H., 1951. Virgin Valley opal district, Humbolt County, Nevada. USA Department of the Interior, Geological Survey Circular, No. 142.
BAUER, M., 1969. Precious Stones. Charles E Tuttle Company, Japan, 373-388.
BROOKS, J.H., 1967. A Prospectors Guide to Opal in the Yowah-Eromanga Area. Queensland Government Mining Journal 68/792, October 1967, 453-458.
CARR, S.G., OLLIVER, J.G., CONOR, C.H.H. & SCOTT, D.C., 1979. Andamooka Opal Fields: The geology of the precious stones field and the results of the subsidised mining program. Geological Survey of South Australia, Report of Investigations 51.
CHIANG, Y.M., BIRNIE, D.P. & KINGERY, W.D., 1997. Physical Ceramics, Principles for Ceramic Science and Engineering. John Wiley and Sons, Inc., New York.
COLE, S.H. & MONROE, E.A., 1967. Electron Microscope studies of the structure of opal. Journal of Applied Physics 38/4, 1872-1873.
CONNAH, T.H., 1967. A prospectors guide to opal in Western Queensland. Queensland Government Mining Journal 67/771, January 1967, 23-39.
CRAM, L., 1998. A journey with colour: a history of Queensland opal 1869-1979. Kingswood Press, Brisbane, Australia.
CSIRO Patent No. 418170, 1964. Opaline materials. Commonwealth of Australia, Patent Specification 50029/64.
DABDOUB, T., 1985. Opal report from Honduras: “the fire still burns”. Tropical Gem Explorations, Metaireie, Louisiana, USA.
DAKE, H.C., FLEENER, F.L. & WILSON, B.H., 1938. Quartz Family Minerals. McGraw Hill Book Company Inc, New York, Ch. 13, 239-254.
DARRAGH, P.J., GASKIN, A.J. & SANDERS, J.V., 1976. Opals. Scientific American 234/4, 84-95.
DARRAGH, P.J., GASKIN, A.J. & SANDERS, J.V., 1977. Synthetic opals. Australian Gemmologist 13/4, November 1977, 109-116.
DARRAGH, P.J., GASKIN, A.J., TERRELL, B.C. & SANDERS, J.V., 1966. Origin of precious opal. Nature 209, No. 5018, 13-16.
DOWNING, P.B., 1992. Opal Identification and Value. First Edition, Majestic Press, Tallahassee USA.
DUDA, R., 1996. Excursion Notes: Field Trip U3 East and Central Slovakia. International Mineralogical Association, Congress Notes 1996.
ECKERT, A.W., 1997. The World of Opals. John Wiley and Sons, Inc, New York.
EYLES, W.C., 1964. The Book of Opals. Charles E Tuttle Company, Japan.
FLÖRKE, O.W., GRAETSCH, H., MARTIN, B., ROLLER, K. & WIRTH, R., 1991. Nomenclature of micro- and non-crystalline silica minerals based on structure and microstructure. Neues Jahrbuch für Mineralogie, Abhandlungen, Stuttgart 163/1, 19-42.
FRITSCH, E. & ROSSMAN, G.R., 1988. An update on colour in gems. Part 3: Colours caused by band gap and physical phenomena. Gems and Gemology 24, 81-102.
FRONDEL, C., 1962. The System of Mineralogy. Seventh Edition, Volume III, Silica Minerals, John Wiley and Sons, Inc. New York, 287-306.
GASKIN, A.J., 1967. Opals. Australian Natural History 15/10, 319-323.
HAWTHORNE, F.C., 1988. Spectroscopic methods in mineralogy and geology. Reviews in Mineralogy 18, Mineralogical Society of America.
HEANEY, P.J., PREWITT, C.T. & GIBBS, G.V., 1994. Silica, physical behaviour, geochemistry, and materials applications. Reviews in Mineralogy 29, Mineralogical Society of America.
HEYLMAN, E.B., 1983. Opal localities in west central Mexico. Lapidary Journal 37/4, 598-602.
HOOVER, D.B., YOHANNES, T.Z. & COLLINS, D.S., 1996 Ethiopia: A new source for precious opal. Australian Gemmologist 19/7, 303-307.
ILER, R.K., 1979. The Chemistry of Silica, Solubility, polymerisation, Colloid and Surface Properties, and Biochemistry. John Wiley and Sons, Inc, New York.
JACKSON, C.F.V., 1902. The opal mining industry and the distribution of opal deposits in Queensland. Queensland Department of Mines Publication 291, 1958, (Reprinted from Publication 177).
JONES, J.B., BIDDLE, J. & SEGNIT, E.R., 1966. Opal genesis. Nature 210, No. 5043, 1353-1354.
JONES, J.B., SANDERS, J.V. & SEGNIT, E.R., 1964. Structure of opal. Nature 204, No. 4962, 990-991.
JONES, J.B. & SEGNIT, E.R., 1971. The nature of opal. 1. Nomenclature and constituent phases. Journal of the Geological Society of Australia 18/1, 57-68.
JONES, J.B. & SEGNIT, E.R., 1972. Genesis of cristobalite and tridymite at low temperatures. Journal of the Geological Society of Australia 18/4, 419-422.
KALOKERINOS, A., 1975. Australian Precious Opals. Thomas Nelson, Sydney, 1975.
KAMMERLING, R.C., KOIVULA, J.I., & FRITSCH, E., (eds). Gem News. Gems and Gemmology. 31/2, 137-138.
KROCH, N.J. & COOPER, W., 1983. Commentary, Queensland Opal. Queensland Department of Minerals and Energy, 15pp.
KUNZ, G.F., 1938. The Curious Lore of Precious Stones. Halcyon House, New York 7th Printing.
LAMBERT, C. & BROWN, G., 1994. A brief report on Indonesian opal. Australian Gemmologist 18/11, 359-361.
LANE, M.E. III, 1983. Microstructural ordering in synthetic opals: An X-ray diffraction and infrared and Raman spectral study. Wichita State University, Msc Thesis, Wichita, USA, 60pp. (unpublished).
LANGER, K. & FLÖRKE, O.W., 1974. Near infrared absorption spectra (4000-9000 cm-1) of opals and the role of water in these SiO2.nH2O minerals. Fortschrite der Mineralogie 52/1, 17-51.
LEECHMAN, F., 1961. The Opal Book. Ure Smith, Sydney.
MacNEVIN, A.A. & HOLMES, G.G., 1979. Notes on precious opal and its occurrence in New South Wales. Geological Survey of NSW, Report GS 1979/268.
MALLORY, L.D., 1969. Opal mining in western Mexico. Lapidary Journal 23/3, 420-428.
McORIST, G.D., SMALLWOOD, A.G. & FARDY, J.J., 1994. Trace elements in Australian opals using neutron activation analysis. Journal of Radioanalytical and Nuclear Chemistry, Articles 185/2, 293-303.
McORIST, G.D. & SMALLWOOD, A.G., 1995. Trace elements in coloured opals using neutron activation analysis. Journal of Radioanalytical and Nuclear Chemistry, Articles 198/2, 499-510.
McORIST, G.D. & SMALLWOOD, A.G., 1997. Trace elements in precious and common opals using neutron activation analysis. Journal of Radioanalytical and Nuclear Chemistry, Articles 223/1/2, 9-15.
MIZUTANI, S., 1970. Silica minerals in the early stage of diagenesis. Sedimentology 15, 419-436.
MONROE, E.A., SASS, D.B. & COLE, S.H., 1969. Stacking faults and polytypism in opal, SiO2.nH2O. Acta Crystallographica A25, 578-580.
MUMME, I.A., SEIBRIGHT, L. & BALL, R., 1975. On the Origin of Volcanic Opal from Houghlahan’s Creek (Near Teven). Australian Gemmologist 12/8, 235-240.
OLLIVER, J.G. & TOWNSEND, I.J., 1993. Gemstones in Australia. Australian Gemstone Industry Council, Australian Government Publishing Service, Canberra, 3-18.
PALMORE, G.D., 1997. The dissolution of calcite and the resulting structural fabric of opal in the Yowah district. BSc(Hons) Thesis, James Cook University of Queensland, Townsville, Queensland. (unpublished).
PEARSON, G., 1985. Role of water in cracking of opal. Australian Gemmologist 15/12, 435-445.
RELPH, R.E. & WHITING, J.N., 1958. The occurrence of precious opal at Lightning Ridge and Grawin with Geological Notes on County Finch. NSW Department of Mines Technical Reports 6, 11-16.
RELPH, R.E., 1959. The White Cliffs opal fields of NSW. NSW Department of Mines Technical Reports 7, 7-17.
ROBERTSON, R.S. & SCOTT, D.C., 1990. Geology of the Coober Pedy precious stones field. Geological Survey of South Australia, Report of Investigations 56.
ROSSMAN, G.R., 1994. Coloured varieties of silica minerals. In: HEANEY, P.J., PREWITT, C.T. & GIBBS, G.V. (eds.) Silica: Physical Behaviour, Geochemistry and Materials Applications. Mineralogical Society of America, Washington DC, USA, Ch.13, 462.
SANDERS, J.V., 1964. Colour of precious opal. Nature 204, No. 4964, 1151-1153.
SANDERS, J.V., 1968. Diffraction of light by opals. Acta Crystallographica A24, 427-434.
SCHUBNEL, H., PINET, M., SMITH, D.C. & LASNIER, B., 1981. La Microsonde Raman en Gemmologie. Association Française de Gemmologie.
SCHEIBNER, E., & BASDEN, H. (eds.) 1998. Geology of New South Wales Volume 2 Geological Evolution. Geological Survey of New South Wales, Memoir geology13/2, p316.
SEGNIT, E.R., ANDERSON, C.A. & JONES, J.B., 1970. A scanning microscope study of the morphology of opal. Search 1/6, 349-351.
SEGNIT, E.R., STEVENS, T.J. & JONES, J.B., 1965. The role of water in opal. Journal of the Geological Society of Australia 12/2, 211-226.
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