Arizona Geological Society


Upcoming events

    • 06 Feb 2018
    • 6:00 PM - 9:00 PM
    • Sheraton, 5151 E Grant Rd. (& Rosemont), Tucson AZ 85712

    Sponsored by:   Available

    Causes of Color in Minerals and Gemstones

    by Paul F. Hlava, Access to Gems and Minerals

    Abstract: The colors that one sees when looking at a mineral or gemstone are due to the response of that person’s eye to the energies of the light coming from the mineral, the emission spectrum of the illumination, and, most importantly, physical phenomena in the material that cause some colors to be absorbed while others are undisturbed or enhanced.  It is beyond the scope of this talk to do more than touch on the physiology of the eye that allows us to see colors.  Likewise, we will not dwell on the emission spectra of various light sources.  Rather, we will concentrate on the various ways in which materials, especially minerals and their heights of perfection - gemstones, produce color from white light.

    Hope DiamondLight is a form of energy (electromagnetic energy) and white light is a mixture of all of the visible energies (or wavelengths).  In order for a mineral to cause color from white light it has to somehow perturb the balance of the light energies.  Kurt Nassau has separated the causes of color into 15 mechanisms based on 5 physical groupings.  While there are some color mechanisms that depend on direct emission of certain colors, most of the mechanisms we are interested in depend on the ability of certain ions in minerals to preferentially absorb certain energies of light.  When these energies are removed from the white light, the mineral is colored by the complimentary color as demonstrated by the CIE* Chromaticity Diagram.

    Light absorption by the electrons of transition metal (or rare earth element - REE) ions, either as major portions of the mineral chemistry or impurities, is one of the most important and well known of the coloring mechanisms.  Most common, rock-forming elements have electronic structures that mitigate against causing colors.  On the other hand, transition metal (and REE) ions have electrons that can be excited to open, higher energy levels.  The electrons gain the necessary energy for the excitation by absorbing a particular energy (color) from white light and thus cause the mineral to show the complementary color.  Three prime examples of this mechanism are rubies, emeralds, and alexandrites, but there are many, many more.

    Star of BombayFluorescence and phosphorescence can be explained as a perturbation of the transition metal absorption model.  In most minerals the electrons return to their ground state by losing infrared energies so the emissions are invisible.  The excited electrons in fluorescent / phosphorescent minerals return to ground state by losing some energies that are in the visible part of the spectrum.  They therefore emit a different color of light from the original.  If this relaxation is quick we call the phenomenon fluorescence.  If the relaxation is slow enough to linger, we call it phosphorescence. 

    Many minerals are dichroic or pleochroic meaning they exhibit different colors in different directions.  These are caused by excited energy levels that are closer or farther apart in different directions.  This, in turn, is controlled by the crystal structure of the mineral squeezing the transition metal ion into an irregular shape.

    The accompanying photos illustrate three examples of coloring mechanism.  Even though both of the stones are blue, the Star of Bombay (lower photo) is colored by intervalence charge transfer with the star caused by scattering, while the Hope Diamond (upper photo) illustrates band gap color.  Both are specimens are from the Smithsonian Institution.

    Bio:  Paul Hlava retired from Sandia National Laboratories in Albuquerque, New Mexico in 2007, after 33 years. He was in the electron microprobe laboratory (as staff member in charge of the lab since 1980) the entire time.  Because the EMP lab is part of the Materials Characterization Department, a centralized analytical facility for Sandia, Paul got to work on a wide variety of prosaic to exotic materials and projects.  He normally analyzed many alloys and joins (welds, brazes, solders, metal/ceramic and glass/metal seals, etc.) but also worked on high tech ceramics, high-temperature superconductors, electronic materials, phosphors, contamination, corrosion, failure analyses, nuclear waste simulants, thermal batteries, et hoc genus omne.  As a result, he has written, co-authored, and/or presented over a hundred papers on a wide variety of materials.  Many of these were given at annual meetings of the Microbeam Analysis Society.  Paul was the Director of the MAS Affiliated Regional Societies and Coordinator of the Tour Speaker Program for almost 28 years, retiring in 2012.

    Paul attended Tulsa University for 2 years and, when the geology program hit a snag, went to the University of Wisconsin at Madison from 1964 to 1967 attaining a BS in geology there.  After 3 years teaching at what is now The U of Wisconsin River Falls campus, he then transferred to the University of New Mexico where he graduated with a geology MS in 1974.  At UNM he worked as a research graduate doing electron microprobe research under Klaus Keil in the Institute of Meteoritics.  He worked on moon rocks, Hawaiian basalts, ultramafic rocks, meteorites, and inclusions in diamonds.  Paul occasionally used his geological and mineralogical expertise on Sandia projects but also did some personal research on minerals.  He has been co-discoverer and co-author on the descriptions of several new mineral species.

    Paul stays active in the area of geology, mineralogy, crystallography, and gemology.  He has been president of the Albuquerque Gem and Mineral Club three times.  He is the Chair for AGMC’s annual spring show (25 or so years now), he acts as the geological/mineralogical/gemology expert for the New Mexico Facetors Guild, and often gives talks on geological/mineralogical/ crystallographic/ gemological subjects.  About twenty five years ago, Paul started a side business, Access to Gems and Minerals, Inc., dealing in gemstones, jewelry, and related items.  This has not only given him access to wholesale rooms full of gemstones but it has piqued his interest in the research side of this field.  He has given several well-received talks on gem related subjects such as this one on the causes of color.

    He is the only/one of the few who turned down the honor of having a mineral named after him.

    • 06 Mar 2018
    • 6:00 PM - 9:00 PM
    • Sheraton, 5151 E Grant Rd. (& Rosemont), Tucson AZ 85712

    Sponsored by:   Available

    Piedras Verdes and Cuatro Hermanos, Sonora, Mexico - A Tale of Two Porphyries

    by Joe Wilkins, Jr., Retired Consulting Geologist

    Abstract:  Two porphyry copper deposits; Piedras Verdes (PV) and Cuatro Hermanos (CH) are located in central and southern Sonora about 150 km apart on NNE-SSW azimuth.  Both have been mapped, sampled, drilled, beginning as the 1900s with activity continuing even today.  A side-by-side comparison of the salient features of the deposit is as follows:

    • Structural Setting - Cortez Terrain, both are in extended and rotated terrains.
    • Basement Host Rocks and intrusions - granodiorite into Jurassic rocks.
    • Breccia Pipes  are present at both deposits.
    • Alteration potassic-sericite-argillic-propylitic and sulfide mineralization are similar
    • K-Ar Age Dates are similar - 67.3 my for Piedras Verdes and about 62-64 my for  Cuatro Hermanos
    • Announced Tonnages and Grades are similar - Piedras Verdes: 316 million tonnes at 0.39% Cu, Cuatro Hermanos:  353 million tonnes at 0.33% Cu plus 0.017% Mo

    However, Piedras Verdes is now an operating copper mine and Cuatro Hermanos is still an interesting deposit.


    Piedras Verdes is situated along a regional developed accommodation zone and has undergone extensive post-depositional structural rotation (including sub-horizontal breccia pipes) and enhanced structurally-induced permeability, which promoted the development of supergene blankets.  The deposit was mapped at 1:10,000 (metric) scale, including lithology, structure, alteration, mineralogy, and FeOx ratios and found to be highly faulted and extended.  Overall, the roots are to the west and top to the east.

    Cuatro Hermanos was also mapped at 1:10,000 scale and also occurs in a rotated and latterly transported terrain.  However, the top of the system is basically intact and upright as indicated by low-angle dips in the intruded volcanic carapace, sub-vertical intrusions and breccia pipes.  Fracturing is mostly confined to veinlets and fault zones.  The overall lack of post-transport permeability precluded the development of significant supergene mineralization.

    The difference between an operating mine at Piedras Verdes and Cuatro Hermanos is the extensive, post-depositional, structural-induced permeability at Piedras Verdes, which is lacking at Cuatro Hermanos.  Also the copper values at Piedras Verdes are derived from supergene copper, which is cheaper to process (heap leaching) than sulfide ores, which require considerable more processing.


    • 01 May 2018
    • 6:00 PM - 9:00 PM
    • Sheraton, 5151 E Grant Rd. (& Rosemont), Tucson AZ 85712

    Sponsored by:   Available

    The Science of Caves and Cave Contributions to Science

    by William B White, Dept of Geosciences, Penn State Univeristy


    Abstract:  Caves have been of interest to humans for millennia, but scientific interest in caves began only in the early 20th Century in the United States and a bit earlier in Europe. Much of the earlier research focused on the caves themselves, how they form, and the processes that take place inside them.  Research of the past few decades has reversed the focus with the interest being in information caves can provide to other parts of the Earth sciences. The talk will provide a broad brush overview of cave sciences in the 21th Century.

    Caves form by two distinct mechanisms. Best known is the top-down dissolution of limestone by circulating ground water made slightly acidic by carbon dioxide. Both equilibrium and kinetics of the reactions are well-known and some elegant models have been made of cave development. A more recent finding is that many caves have formed by deep-seated solutions welling up to the water table with the active agent being sulfuric acid rather than carbonic acid.

    Many caves display spectacular speleothems but the bulk mineralogy tends to be boring: calcite, gypsum, and aragonite. Although less obvious, more than 300 other minerals have been formed by secondary deposition in caves.

    What brought cave studies into the mainstream of the Earth sciences is the importance of karst aquifers as water supplies. Karst aquifers are a major source of domestic water supply. The conduit permeability means that karst aquifers respond rapidly to flood flows with changes in flow paths and water levels. Contaminant transport in karst aquifers is rapid, often to unknown destinations, and strongly dependent of the physical properties of the contaminant.

    Caves have been recognized as useful sources of geomorphic information. Caves are strongly linked to landscape evolution. Clastic sediments in caves can be dated by cosmogenic isotopes providing useful markers for incision rates of surface streams and landscape evolution.

    Calcite stalagmites grow slowly from the bottom up. A precise chronology of the layers can be obtained by U/Th isotope dating methods. Isotopic signatures (O,C,H) and trace element concentrations can be mapped along the growth axis.  These maps reveal climatic variations of the surface above the cave over the time span represented by the speleothem.

    Bio:  William B. (Will) White is professor emeritus of geochemistry in the Department of Geosciences at the Pennsylvania State University. Prior to retirement he held joint appointments in Geosciences and in the Materials Research Institute. He also taught in the Department of Materials Science and Engineering and supervised graduate students in the interdisciplinary program in Environmental Pollution Control. He holds a B.S. degree in chemistry from Juniata College (Huntingdon, PA) (1954). From 1954 to 1958 he was on the staff of the Department of Research in Chemical Physics at the Mellon Institute in Pittsburgh while pursuing graduate study in physics at the University of Pittsburgh. In 1958 he transferred to Penn State, received his Ph.D. in geochemistry in 1962, and after a year and a half in a post-doctoral position, joined the faculty in 1963, reaching the rank of full professor in 1972.

    Dr. White received the Matthew J. and Anne C. Wilson Award for outstanding teaching from the College of Earth and Mineral Sciences in 1974, the Outstanding Service Award (Honorary Life fellow) from the National Speleological Society in 1975, and the Lifetime Achievement Award in the Science of Speleology from the NSS in 1994. In 2001 he received the Karst Waters Institute Award and in 2004 the Distinguished Career Award from the Quaternary Geology and Geomorphology Division of the Geological Society of America. He is a Fellow of the American Association for the Advancement of Science, The Mineralogical Society of America, The American Ceramic Society, and the National Speleological Society. Dr. White's research activities have been divided between materials science and geological science. The former includes investigations of crystal chemistry, glass science, optical and phosphor materials, and infrared, Raman, and luminescence spectroscopy. The geological sciences include mineral physics and the hydrogeology and geomorphology of caves and karst. Overall, the research has been reported in 440 technical papers and 15 books. Recent books include "The Encyclopedia of Caves" (Elsevier, 2012), "The Caves of Burnsville Cove, Virginia" (Springer, 2015), and "Caves and Karst of the Greenbrier Valley in West Virginia" (Springer, 2015).   His textbook on Geomorphology and Hydrology of Karst Terrains (Oxford Univ Press 1988) has been widely used.

    Field investigations for cave and karst studies include the Appalachians (Pennsylvania to Alabama), the Mammoth Cave area, Kentucky, Puerto Rico, and other locations. Dr. White has traveled widely to karst areas of the world including much of the United States, parts of western Europe, the Adrian Coast and China.

Past events

02 Jan 2018 Peter L. Ward presents Bringing Peace to the Climate Wars
05 Dec 2017 Joellen Russell presents The Ocean's Role in the Climate of the Anthropocene
07 Nov 2017 Eric Sundquist presents Geological Perspectives on Carbon Dioxide, the Carbon Cycle and Carbon Management
03 Oct 2017 Lily Jackson presents Andean River Sediments as a Window into the Tectonic History of Ecuador
05 Sep 2017 Vic Baker presents The Influence of the 18th Century Enlightenment on the Natural Sciences
22 Aug 2017 AGS Meet and Greet, A Networking Event
11 Jul 2017 Andrew Zaffos presents Global Tectonics and Marine Animal Diversity
06 Jun 2017 Dan Johnson presents Introduction to the Florence Copper Project and In-Situ Copper Recovery
02 May 2017 Robert Glennon presents America's Water Crisis and What To Do About It
22 Apr 2017 Spring Field Trip - The Laramide-age Chilito Porphyry Copper Deposit
04 Apr 2017 David London presents The Nature and Origins of Internal Zonation within Granitic Pegmatites
07 Mar 2017 Derek J. Thorkelson presents The Precambrian Tectonic Connection between Yukon and Arizona
07 Feb 2017 Daniel Hummer presents Mineral ecology and evolution: Using large datasets to tell the story of the co-evolution of Earth and life
03 Jan 2017 David A. Sawyer presents Dating Geologic Time in the Cretaceous: Integrating Biostratigraphy, Isotope Geochronology, and Astrochronology in Sedimentary Deposits of the Cretaceous Western Interior Seaway
06 Dec 2016 John W. Ewert presents USGS Responses to Some Volcanic Crises and Eruptions Around the World
01 Nov 2016 Alexander Schauss presents Minerals, Trace Elements and Human Health
22 Oct 2016 Fall Field Trip - The Peach Spring Tuff and the Silver Creek Caldera, Northwestern Arizona
04 Oct 2016 Hamish Martin Presents Geology of the Resolution Cu-Mo Deposit, Superior Arizona
06 Sep 2016 Keith R. Long Presents No Bonanza from Cheap Oil
02 Aug 2016 Lee Allison Presents The Future of State Geological Surveys: the Arizona Case Study
05 Jul 2016 Don Applebee Presents Genesis of the Chilito Porphyry Copper Deposit
07 Jun 2016 Robert Hildebrand Presents Collisions, Slab Failure Magmatism and the Development of Cordilleran Batholiths
03 May 2016 Peter Modreski will present "Pegmatites: Mineralogy, Gemstones, Economic Geology, and maybe not quite the same Giant-Crystal Rocks you always thought they were"
30 Apr 2016 Spring Field Trip - An Introduction to the Pinal Schist in Southeastern Arizona
05 Apr 2016 Jordon Bright Presents Looking for an Ocean in the Desert, the Enigmatic Bouse Formation
01 Mar 2016 Peter R. Johnson Presents Tectonics and Mineral Deposits of the Arabian-Nubian Shield
02 Feb 2016 Dr. Karen Wenrich Presents The Ga-Ge Rich Apex Mine, Utah - A Tsumeb, Namibia Analogue
05 Jan 2016 Sarah Baxter Presents Calc-silicate Alteration and Ore Characterization, ASARCO Mission Complex, Pima County, Arizona
01 Dec 2015 Peter Smith Presents The Latest News from Mars
14 Nov 2015 Fall Field Trip - Northern Plomosa Mountains and Bouse Formation in Blythe Basin
03 Nov 2015 Karen Kelley presents The Giant Concealed Pebble Cu-Au-Mo Porphyry Deposit, Southwest Alaska
06 Oct 2015 Caleb King presents Eocene Hydrothermal Systems and Contrasting Hydrothermal Alteration in the Battle Mountain District, Nevada
01 Sep 2015 Carl Bowser presents The Genesis of the Kramer Borax Deposit, Rogers Lake, Mojave Desert, CA:
04 Aug 2015 Dan Lynch presents Volcanoes in the Back Yard
07 Jul 2015 Erik Melchiorre presents The Complex Geological History Recorded by Arizona Placer Deposits:
02 Jun 2015 Jan C. Rasmussen Presents - Arizona Mineralization through Geologic Time
05 May 2015 Gordon Haxel Presents - Alpine peridotite in the desert - Arizona's Laramide subduction complex
02 May 2015 Spring Field Trip - Oak Creek - Mormon Lake Graben
18 Apr 2015 Third Annual Arizona Geological Society Doug Shakel Student Poster Event
03 Mar 2015 Apollo 17 Astronaut and Former Senator Harrison H. Schmitt presents A Geological Visit to a Valley on the Moon
03 Feb 2015 Don Yurewicz Presents Assessing Unconventional (Continuous) Hydrocarbon Resource Plays
06 Jan 2015 Arend Meijer presents: Sulfide-rich Proterozoic Mafic Rocks and Arizona Porphyry Copper Deposits - A Connection?
02 Dec 2014 Victor R. Baker: Megafloods on Earth, Mars, and Beyond
15 Nov 2014 Fall Field Trip - Debris Flows Shape the Sabino Canyon Landscape - look out below!
04 Nov 2014 Isabel F. Barton: Historical Development & Current State of Geological Research in the Central African Copperbelt
07 Oct 2014 Apollo 17 Astronaut and Former Senator Harrison H. Schmitt presents A Geological Visit to a Valley on the Moon
02 Sep 2014 Lewis Land presents Evaluation of Groundwater Residence Time in a Karstic Aquifer System
05 Aug 2014 Jamie Molaro presents Thermal Stress Weathering in the Inner Solar System
01 Jul 2014 Jim Leenhouts presents Surface-water/groundwater Interactions in Arizona
03 Jun 2014 Arend Meijer presents Pinal Schist of So. Arizona--A Paleoproterozoic Fore-Arc Complex
06 May 2014 John C. Lacy presents The Genesis of Mining Law
26 Apr 2014 Spring Field Trip - Geology of the Christmas Porphyry Copper Deposit
24 Apr 2014 Second Annual Arizona Geological Society Doug Shakel Student Poster Event
01 Apr 2014 Eric Seedorff presents, Structural Dismemberment of a Porphyry Molybdenum System, Spruce Mountain District, Northeastern Nevada
04 Mar 2014 John Dreier presents, Copper Deposits of the Coast Ranges of Chile; A trip through time, space, and ore deposit nomenclature
04 Feb 2014 Ralph Stegen presents The Morenci Porphyry Cu-Mo Deposit, Greenlee County, Arizona: A Geologic Summary with Emphasis on Hypogene and Supergene Mineralization
07 Jan 2014 Steve Castor presents, Mountain Pass and other North American Rare Earth Element Deposits
03 Dec 2013 Stephen Jackson, USGS, Looking forward from the past: Ecological impacts of climate change through the lens of history
05 Nov 2013 Malcolm Siegel, PhD, MPH, LJS Consulting, Inc and School of Medicine, University of New Mexico, Albuquerque, NM. 87047: Uranium Mining in the American Southwest: Can Medical Geologists Ask the Right Questions?
04 Oct 2013 Field Trip - H. Wilson Sundt Generating Station
01 Oct 2013 Mark Logsdon, Principal Geochemist, Geochimica, Inc.: What Does “Perpetual” Management and Treatment Mean? Toward a Framework for Determining an Appropriate Period-of-Performance for Management of Reactive, Sulfide-Bearing Mine Wastes
01 Oct 2013 Mark J. Logsdon, Geochimica, Inc., Does acid-rock drainage lead to waste-rock instability? Geological, hydrological, and geochemical framework for the Questa Mine
03 Sep 2013 Pete Reiners, UA, Geosciences Dept., Geochronology of secondary Fe & Mn oxides in bedrock
30 Aug 2013 Field Trip - University of Arizona Tree-Ring Research Laboratory
06 Aug 2013 Bill Stavast, Freeport-McMoRan Copper & Gold, The Safford Mine: What we have learned since production began
02 Jul 2013 Lukas Zurcher, USGS, presents: "Tectono-magmatic evolution of the Central Tethys Region"
04 Jun 2013 Steve Van Nort presents, "Gold Fever! The BRE-X/Busang Story
07 May 2013 Federal lands and mineral resources: Colorado Plateau uranium deposits and the Sonoran Desert Heritage
18 Apr 2013 First Annual Arizona Geological Society Doug Shakel Student Poster Event

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