Historical Reading List: Benitoite — the California State Gemstone

A collection of faceted benitoite gemstones (approximately 5 carats total weight). Gift of Benitoite Mining Co. Photo by: Orasa Weldon/GIA.
A collection of faceted benitoite gemstones (approximately 5 carats total weight). Gift of Benitoite Mining Co. Photo by: Orasa Weldon/GIA.

Early in 1907 crystals of a rare mineral new to science, and subsequently named benitoite, were discovered in the Coast Ranges of California along the border of San Benito and Fresno counties at a locality in the New Idria Mining District about 100 miles southeast of San Francisco.  The mineral had high refractive indices and optical dispersion, a vitreous luster, and strong dichroism. The most striking feature of these new crystals was their blue color – when cut properly as gemstones, they could rival blue sapphire in color and excel it in brilliancy.  Although subsequently found in small amounts elsewhere, the California occurrence has produced the greatest number and best-quality crystals.  On October 1, 1985, benitoite was designated the California’s official gemstone.  It is interesting to note that, in spite of several investigations, the cause of the mineral’s blue color remains elusive.


This reading list was compiled to give you an opportunity to learn more about benitoite. The list is not comprehensive, but a compilation of some interesting information that has often been forgotten or overlooked

Many of the articles exist in the public domain and can be found online at digital libraries such as Hathitrust, Internet Archive, or other digital repositories. More recent publications can often be found in libraries, including the Richard T. Liddicoat Gemological Library. Abstracts of these articles can usually be found on the website of the original journal or magazine, and the article itself is often available for purchase from the publisher.

Regarding the GIA library’s holdings and on-site access, please contact the GIA library in Carlsbad.

Benitoite, a New California Gem Mineral, G.D. Louderback and W.C. Blasdale, University of California Publications – Bulletin of the Department of Geology, Vol. 5, No. 9, pp. 149-153, (1907).  This publication, the first description of benitoite, gives basic information on the characteristics and properties of this new mineral.  A chemical analysis of the mineral, a barium-titanium silicate, is included.  A summary of this publication appeared in Mining and Scientific Press, Vol. 95, No. 6, p. 175, (1907), and in the Zeitschrift für Kristallographie, Vol. 46, No. 4, p. 386, (1909).

Notes on the Occurrence of the Recently Described Gem Mineral, Benitoite, R. Arnold, Science, New Series, Vol. 27, No. 686, pp. 312-314, (1908). The mode of occurrence of benitoite is described.  It is found, along with black crystals of neptunite, in veins of a white zeolite (natrolite) within small bodies of glaucophane schist that occur within a large area of serpentinite.

Interpretation of the Chemical Composition of the Mineral Benitoite, E.H. Kraus, Science, New Series, Vol. 27, No. 696, pp. 710-711, (1908). The author points out some similarities between benitoite and beryl.

The Chemical Formula of the Mineral Benitoite, W.C. Blasdale, Science, New Series, Vol. 28, No. 712, pp. 233-234, (1908). A discussion of the correct chemical formula – BaTiSi3O9 – is presented.

Note on the Crystal Form of Benitoite, A.F. Rogers, Science, New Series, Vol. 28, No. 722, p. 616, (1908). The author suggests that benitoite displays a crystal form that places it in one of the 32 possible symmetry classes – the ditrigonal dipyramid – that previously had not been recognized among crystallized minerals.

Bemerkungen ueber die Krystallklasse des Benitoit [Remarks on the Crystal Class of Benitoite], C. Hlawatsch, Tschermaks Mineralogische and Petrographische Mitteilungen, Vol. 28, pp. 178-181, (1908).  This article also discusses the unusual crystal symmetry of benitoite.
Benitoite, its Paragenesis and Mode of Occurrence, G.D. Louderback and W.C. Blasdale, University of California Publications – Bulletin of the Department of Geology, Vol. 5, No. 23, pp. 331-380, (1909). This report provides a detailed description of the physical and chemical properties, mode of occurrence, and geologic conditions of formation of benitoite.

Über die Winkelverhältnisse des Benitoit [The Angular Relationships of Benitoite], H. Baumhauer, Centralblatt für Mineralogie, Geologie und Paläontologie, pp. 592-594, (1909). The author makes a study of the angular relationships among crystal faces observed on benitoite.

Bemerkungen über den Benitoit [Remarks on Benitoite], C. Hlawtsch, Zeitschrift für Kristallographie, Vol. 46, No. 6, pp. 602-603, (1909). Some comments are presented on the crystal morphology of benitoite.

Note on the Crystal Form of Benitoite, C. Palache, American Journal of Science, Vol. 127, No. 161, p. 398, (1909).  Examination of additional crystals confirms of A.F. Rogers’ earlier conclusion of the correct crystal class of this mineral. The same information is published in the Zeitschrift für Kristallographie, Vol. 46, No. 4, p. 379, (1909).

Die Krystallform des Benitoits [The Crystal Form of Benitoite], C. Hlawatsch, Separat-Abdruck aus dem Centralblatt für Mineralogie, Geologie und Paläontologie, No. 10, pp. 293-302 and 410, (1909). The author gives a description of the crystal morphology of benitoite.

Mines and Mineral Resources of the Counties of Monterey, San Benito, San Luis Obispo, Santa Barbara and Ventura, W.W. Bradley, E. Huguenin, C.A. Logan and C.A. Waring, California State Mining Bureau, Fifteenth Report of the State Mineralogist for 1915-1916, 183 pp., (1917). This state publication contains a section on pages 42-43 on the occurrence of benitoite.

Lauediagramme des Benitoit [The Laue Diagram for Benitoite], F. Rinne, Centralblatt für Mineralogie, Geologie und Paläontologie, Section A, pp. 193-201, (1919). Results are presented of an Xray diffraction study that confirmed the crystal symmetry class for benitoite.

Über die Struktur des Benitoits [On the Structure of Benitoite], J.J.P. Valeton, Fortschritte der Mineralogie, Vol. 12, pp. 91-92, (1927). Article not seen.

Röntgenographische Untersuchung von Benitoit [Radiographic Examination of Benitoite], B. Gossner and E. Mussgnug, Centralblatt für Mineralogie, Geologie und Paläontologie, Section A, No. 9, pp. 304-310, (1927).  Article not seen.

The Crystal Structure of Benitoite, BaTiSi3O9, W.H. Zachariasen, Zeitschrift für Kristallographie, Vol. 74, No. 2, pp. 139-146, (1930). Using the Laue X-ray method, the author solves the crystal structure of benitoite – the unit cell dimensions and the placement of the atoms within that cell.

Benitoite, Neptunite, and Joaquinite, E.V. Van Amringe, Oregon Mineralogist, Vol. 2, No. 11, pp. 9-10, (1934).  Article not seen.

Benitoite – California’s Exclusive Gem, M.P. Yaeckel, Oregon Mineralogist, Vol. 2, No. 10, pp. 26-27, (1934).  Article not seen.

Benitoite, One of the Rarest Gems, A.H. Frank, Lapidary Journal, (June), p. 567, (1935).  Article not seen.

Benitoite, a Rare Gemstone, J. Melhase, The Mineralogist, Vol. 6, No. 11, pp. 7-8 and 27-29, (1938).  Article not seen.

Gem Lore: Story of a Gemstone Christening, G.H. Marcher, The Mineralogist, Vol. 7, No. 5, p. 200 and 217-219, (1939).  Article not seen.

Minerals of the Serpentine Area in San Benito County, California, A. Pabst, Rocks & Minerals, Vol. 26, No. 9/10, pp. 478-485, (1951). Various mineral localities, including the benitoite deposit, that occur in the large serpentinite body in the mountainous area of the county.

On the Synthesis and Hydrothermal Stability of Benitoite, D.E. Rase and R. Roy, American Mineralogist, Vol. 40, No. 5/6, pp. 542-544, (1955). The authors present the results of the hydrothermal growth of benitoite, and they fix its upper stability limit as a mineral phase at 965°C ± 10°C at a pressure of 5000 pounds per square inch (psi).

The Story of Benitoite – The World’s Rarest Gem, L. Quick, Lapidary Journal, Vol. 10, No. 6, pp. 510-518, (1957). General information is given on benitoite as a gem mineral.

“Gemstones of North America”, J. Sinkankas, Vol. 1, pp. 471-473, Van Nostrand Reinhold, New York, (1959), Vol. 2, pp. 280-288, (1976) and Vol. 3, pp. 27-31, (1997). A description is given of the occurrence and properties of benitoite.

The Benitoite Story, O. Couch, 10 pp., (1961).  Booklet available in the GIA Library.

Paramagnetic Resonance of Fe3+ in Benitoite, S.P. Burley and G.J. Troup, British Journal of Applied Physics, Vol. 16, No. 3, pp. 315-318, (1965).  A scientific study of defects in the atomic structure of benitoite.

Minerals of Southern San Benito County, California, W.P. Moller, Gems & Minerals, No. 331, pp. 28-32, (1965).  Article not seen

Collecting Fluorescent Minerals, R.W. Jones, Rocks & Minerals, (June), pp. 430-432, (1967). A discussion of the fluorescence behavior of benitoite.

Verfeinerung der Kristallstruktur von Benitoit BaTi[Si3O9] [Refinement of the Crystal Structure of Benitoite BaTi[Si3O9]], K. Fischer, Zeitschrift für Kristallographie, Vol. 129, No. 1/4, pp. 222-243, (1969).  Using powder and single-crystal X-ray diffraction data, the author confirms the original crystal structure determination made by W.H. Zacharaisen.

Mineralien des San Benito County, Zentral-Kalifornien [Minerals of San Benito County, Central California], U. Borner, Der Aufschluss, Vol. 22, No. 12, pp. 377-389, (1971).  A general report is given on the minerals, including benitoite, that can be found in San Benito County.

Chemical Composition and Physical, Optical and Structural Properties of Benitoite, Neptunite and Joaquinite, J. Laird and A.L. Albee, American Mineralogist, Vol. 57, No. 1/2, pp. 85-102, (1972). The authors characterize these three rare titanium silicate minerals that occur together in natrolite veins in metamorphic glaucophane schist near New Idria in San Benito County.

Das Absorptionsspektrum des Benitoits im Nahen Ultarot [The Absoprtion Spectrum of Benitoite in the Near Infrared], A. Beran, Tschermaks Mineralogische und Petrographische Mitteilungen, Vol. 21, No. 1, pp. 47-51, (1974).  Spectroscopic study of an inclusion-free colorless crystal showed a broad, distinctly pleochroic, absorption band centered at 3030 wavenumbers in the near-infrared spectrum.  This water-related band disappears if the crystal is heated to 400°C.  The authors suggest this implies the presence of water molecules in the structure.

La Benitoite [Benitoite], P. Bancroft, Le Monde et Minéraux, No. 11, pp. 258-261, (1976).  Article not seen.

Single-Crystal Vibrational Spectrum of Benitoite, a Non-Centrosymmetric Silicate Crystal, and Some Comments on Beryl, D.M. Adams and I.R. Gardner, Dalton Transactions, No. 4, pp. 315-321, (1976).  A spectroscopy study of the benitoite atomic structure.

Minerals of the Benitoite Gem Mine, W.S. Wise and R.H. Gill, Mineralogical Record, Vol. 8, No. 6, pp. 442-452, (1977). A description is given of the minerals found with benitoite at the gem mine.

The Fluorescence of Benitoite, K. Mitchell, Journal of Gemmology, Vol. 17, No. 3, p. 149, (1980). Benitoite has long been known to emit bright blue fluorescence to short-wave ultraviolet light.  The author reports that colorless and pale blue samples also display a dull red fluorescence to long-wave ultraviolet radiation – this luminescence diminishes as the color of the mineral becomes more intense blue.

Synthése Hydrothermale de la Bénitoite [Hydrothermal Synthesis of Benitoite], M. Christophe, G. Gouet and J. Wyart, Bulletin de Minéralogie, Vol. 103, pp. 118-119, (1980). Article not seen.

Faceting Benitoite, E.R. Bancroft, Gems & Minerals, (July), pp. 23-24, (1985).  Article not seen.

California’s New Official Gem, Benitoite, D. Dupras, California Geology, Vol. 39, No. 1, pp. 3-4, (1986).  Article not seen.

Benitoite, W. Wight, Canadian Gemmologist, Vol. 7, No. 3, pp. 78-81, (1986). A description of the gemological properties of benitoite.

The Benitoite Story, D.H. Austin, 80 pp. (1988).   Booklet available in the GIA Library.

A Rare Bit of History, S. Frazier and A. Frazier, Lapidary Journal, Vol. 44, No. 8, pp. 46-58, (1990). The authors review the history of discovery of benitoite, and discuss the larger faceted gemstones that have been fashioned from this material.

A Benitoite Bibliography, S. Frazier and A. Frazier, Lapidary Journal, Vol. 44, No. 8, pp. 61-68, (1990).  The authors list publications on this mineral.

Benitoite Mining Today, M. Gray, Canadian Gemmologist, Vol. 7, No. 3, pp. 82-83, (1986), and Recent Developments at the Benitoite Mine, Canadian Gemmologist, Vol. 13, No. 4, pp. 118-119, (1992). Two brief reports by the same author on the operations at the Dallas Gem Mine.

The Crystal Chemistry of the Benitoite Group Minerals and Structural Relations in (Si3O9) Ring Structures, F.C. Hawthorne, Neues Jahrbuch für Mineralogie, Monatshefte, No. 1, pp. 16-30, (1987).  The author reviews the crystal chemistry and structural similarities of benitoite and several related minerals.

Four American Beauties, J.C. Zeitner, Lapidary Journal, Vol. 41, No. 4, pp. 34-41, (1987). The author describes four American gemstones including benitoite.

Paramagnetic Defects in Benitoite, A.B. Vassilikou-Dova and K. Eftaxias, Zeitschrift für Naturforschung A, Vol. 46, pp. 579-582, (1991).  A scientific study of defects in the atomic structure of benitoite.

Raman Spectroscopy of Silicate Rings: Benitoite and the Three-Membered Ring, D.A. McKeown, M.I. Bell and C.C. Kim, Physical Review B, Vol. 48, No. 22, pp. 16357-163365, (1993).  The Raman spectroscopy method provides information on the rings of silicate tetrahedra that form an important part of the benitoite crystal structure.  A similar article by these authors appeared in Physical Review B, Vol. 47, No. 13, pp. 7869-7877, (1993).

Connoisseur’s Choice – Benitoite, San Benito County, California, R.B. Cook, Rocks & Minerals, Vol. 69, No. 6, pp. 392-395, (1994). According to the author, of all the exceptionally rare minerals, benitoite is perhaps the most beautiful.  Although best known for its blue color, the mineral has also been as white, pink, various shades of purple, as well as colorless and transparent crystals.  Crystals up to 2 inches long across have been found.

Geology and Mineralogy of the New Idria District, San Benito and Fresno Counties, California, W.S. Wise and W.P. Moller, Rocks & Minerals, Vol. 70, No. 1/2, pp. 30-35, (1995). The authors describe the geologic setting and mineral deposits on the mining district, which lies at the southern end of the Diablo Mountain Range.  The mineral deposits occur within a large block of serpentine that was emplaced into geologically younger sedimentary rocks.

Benitoite from the New Idria District, San Benito County, California, B.M. Laurs, W.R. Rohtert and M. Gray, Gems & Gemology, Vol. 33, No. 3, pp. 166-187, (1997). The history of the discovery of benitoite, and its occurrence in the New Idria District, are discussed in some detail by the authors.  Results are also presented from gemological data collected on 139 benitoite samples.

Blue Bounty, K. Woods, Colored Stone Magazine, Vol. 14, No. 5, pp. 32-33, (2001).  A short article on benitoite mining.

Migration of the Mendocino Triple Junction and the Origin of Titanium-rich Mineral Suites at New Idria, California, M.R. van Baalen, International Geology Review, Vol. 46, No. 8, pp. 671-692, (2004). The New Idria area is noted for the occurrence of benitoite and other titanium-rich minerals.  The author suggests these minerals formed by metamorphism of pre-existing pyroxenite veins within the larger block of serpentinite.  Benitoite is thought to have formed along the contact zone between tectonic blocks of greenstone and blue-schist.

The Nature of Blue Luminescence from Natural Benitoite, BaTiSi3O9, M. Gaft, L. Nagli, G. Waychunas and D. Weiss, Physics and Chemistry of Minerals, Vol. 31, No. 6, pp. 365-373, (2004).  The blue luminescence results from intrinsic luminescence for isolated TiO6 octahedra in the crystal structure.

The Nature of Red Luminescence of Natural Benitoite, BaTiSi3O9, M. Gaft, L. Nagli, G. Waychunas and G. Panczer, Mineralogy and Petrology, Vol. 85, No. 1/2, pp. 33-44, (2005).  The red luminescence appears to be due to two causes - activation by Ti3+ along with either Cr3+ or Mn4+.

Collecting Benitoite is Back!, M. White and H. White, Rock & Gem, Vol. 37, No. 11, pp. 28-32, (2007). A report on collecting benitoite at the gem mine.

The 100-Year History of the Benitoite Gem Mine, San Benito County, California, W.E. Wilson, Mineralogical Record, Vol. 39, No. 1, pp. 13-42, (2008). This article presents the most complete discussion of the history of the gem mine; it includes many historic and recent photos of the mine site and benitoite mineral specimens.

Dr. James Shigley is a distinguished research fellow at the Gemological Institute of America in Carlsbad, California.