Friday, July 18, 2014

Wulfenite from the Rowley Mine, Arizona

Wulfenite on barite, Rowley mine

Wulfenite - lead molybdate (PbMoO4) and mimetite (Pb5(AsO4)3Cl) on barite (BaSO4). This specimen was dug a few years ago by a friend of mine at the famous Rowley mine at Theba, Arizona. Wulfenite forms extraordinarily beautiful bladed crystal clusters, often in vivid shades of reddish-orange or yellow-orange.  The smaller, rounded crystals at the base of the Wulfenite blades are likely mimetite, a lead arsenate chloride that often co-occurs with wulfenite at this location, though mimetite from this mine is usually more yellow and spindly.  The larger rock on which both crystals occur is barite, or barium sulfate.  Because these are heavy metal rich rocks containing arsenic and lead, despite their beauty, they are not suitable for young children, and it is probably smart to wash your hands after handling them in your collection.  These crystals are also quite delicate, and require special care in display.  Mimetite, in particular, is easily crushed to a fine powder, as a friend pointing at one of my best specimens once accidentally demonstrated.  If you would like to learn more about any of these minerals or about the mine from which they came, here are a few links:  the wikipedia page for wulfenite is particularly good: and here is some information on the Rowley Mine:  Here is the wikipedia page for mimetite: and here are the  and Wikipedia links for barite:  and

Wednesday, July 16, 2014

Sedimentary Geology Basics

I was speaking with an acquaintance a couple of days ago, and he mentioned that all three of his children were following his footsteps, after the completion of their university degrees, into the field of geology.  Two had already graduated and entered the field, and the third was about to.  It occurred to me that children of geologists have a tremendous advantage entering the field, since they learn a lot of the fundamentals just from the way their parents talk about the rocks around them as they are growing up.  Because of their experience and training, there are certain assumptions that geologists make when looking at rocks.  It is easy to forget that other people don't immediately make these assumptions.  This picture is of a spring that I walk by on my way to work each morning.  I've tried to capture, in a simple graphic, several of the absolute basics of sedimentary geology.  Sedimentary rocks are layered, and the layers have names.  These layers are usually more-or-less horizontal, at least to start with.  Unless they've been tossed around somehow, the oldest ones are on the bottom, and younger ones are on the top. Layers in rock are generally called strata (plural stratum).  The study of rock layers is 'stratigraphy.'  Minor layers in the rock are called bedding planes, and may represent changes in tides, storms, or longer term events.  These don't necessarily have names.  Larger groups of these minor layers are named as 'members,' and groups of members make up 'formations.'  Members and formations are formal 'lithostratigraphic units,' and these represent distinctive, recognizable groups of rocks that are roughly the same age and typically share something significant in common in terms of their composition and appearance.  The concept that rocks are grouped and that the groups have names is absolutely key if a person wants to learn about the rocks in their area.  Knowing the name of a rock unit allows you to research everything that has been learned and published about it through the cooperative work of generations of scientists.  Here is a link to an explanation of lithostratigraphic rock units, published by the International Commission on Stratigraphy:  and here is a link to a wikipedia page discussing the concept of a geological 'formation,' the dominant unit in stratigraphic study:

Sunday, July 13, 2014

Ripple Marks at Cairns Australia

Have you ever seen a cross section of ripples similar to this in rocks exposed in a road cut along the side of a road?  When these kinds of structures are preserved in layered sedimentary rocks, geologists call them 'bed forms.'  By cataloging variations in the shape and size of these structures where they occur in modern active environments, researchers have come to understand the specific circumstances under which different variations form.  Through this work, they have become a useful tool in understanding the environment in which the sediments that have been preserved in ancient rocks were deposited.  Sedimentary geologists can recognize the difference between ripples produced by wind or water, can tell whether sand or clay was deposited in a river, a delta, or in the sea, can distinguish different speeds and directions of water flow, and can also tell whether water changed directions periodically or was influenced by significant wave activity on the surface.  In case you would like to learn more, here is a link to a youtube video of a typical flume experiment (a tank in which water flows over sediment in a controlled setting) in which you can see the formation and migration of ripples:  and here is a link to the Wikipedia page associated with bedforms:

Saturday, July 12, 2014


Malachite Cabochon

This is probably the cutest malachite cabochon I've ever seen, but how the face got there is even more interesting than how adorably happy it looks.  The interesting banding and rounded forms that one often sees in malachite are the result of how the mineral grows.  Ground water, interacting with rich copper deposits, typically produces a zone of complex minerals surrounding the copper-rich ore zone.  Malachite is one of these minerals.  It is a copper carbonate Cu2CO3(OH)2.  Like the more familiar carbonate mineral that we know as limestone, which forms most instances of stalactites and stalagmites in caves, malachite frequently forms by precipitation from groundwater in open voids in the ground.  The resulting crystals can be botryoidal to stalagmitic masses, which, when cut, show concentric rings, much like one would see if they cut through a slow-growing stalagmite in a typical cave. (...Though cutting up stalagmites in caves is something you should never do.)  The bands of color represent minor differences in chemistry of the groundwater as the crystalline mass of malachite grew outward.  In case you would like to learn more, here is a link to the mindat page for malachite:  And here is a link to malachite on Wikipedia:

Friday, July 11, 2014

Spencer Idaho Opal Tiara

Spencer Idaho Opal Tiara

Though Australia is the best known opal producer in the world, there are really quite a large number of places that produce at least limited quantities of precious opals.  Mexico is famous for its red-based fire opals, the Virgin Valley region of Nevada produces beautiful fiery opal limb casts, with opal replacing wood once buried beneath ashy soil in highland lakes, and a new major source of the gemstone has recently emerged in Ethiopia.  I made the crown above using sterling silver and, if I recall correctly, 27 opal triplets from Spencer, Idaho.  This is how I've been making my living for a couple of decades now, and more importantly, its how I pay my way (sporadically) through a PhD program and afford to do a little science.  This piece represents about 60 hours of work.  Here is one of many (nearly randomly chosen) links to the Spencer area opal mines in case you would like to learn more about these amazing stones:

Thursday, July 10, 2014

Introduction and a Few Nice Fossils

First Post: Introduction and a Few Nice Fossils

Hi!  and Welcome.  This is my first attempt at building a blog, so please pardon if it is a bit clumsy at first.  I've wanted to do something like this for some time, but just haven't quite known how.  ...We'll see how long it takes to figure out.  For now, I'll dive right in.

I work with rocks, fossils and minerals in a number of capacities.  Most visibly, I buy and sell them in my retail business and study them as a research scientist.  I also write about them, collect them, make jewelry out of them and, as frequently as possible, go into the field to dig them up for fun, science or profit.  I also enjoy sharing my passion for this and other subjects with other people that enjoy learning about the complex and fascinating world around them.  This is the purpose of the blog.  I hope you enjoy it!

An assortment of fossil fish that we quarried around 2008 from the Eocene Green River Formation in Wyoming, one of the world's premier fossil localities.  I shot this picture while selling rocks, fossils and my own jewelry work at the Tucson Gem Show in Arizona shortly afterwards.  If you'd like to learn more, here is a link to the Fossil Butte National Monument, near the private quarry in which I was working.  and here is a link to the associated Wikipedia page