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Monday, January 10, 2011

Judgmental Gemstones? A Corundum Conundrum

Colorful gemstones were long a trademark of royalty and stature in ancient cultures. Notwithstanding the shear rarity of precious jewels, the pure, monochromatic radiance of a top-quality gemstone distinguished it from the chaotic and visually unbecoming vulgarity of the ore-body matrix in a way that royalty could truly appreciate.

Modern jewelers and mining efforts have since made rubies, sapphires, emeralds, and other stones available to a more "common" clientelle, but these geologic wonders never lost their sanctifying quality. Owning and being adorned by (or, for that matter, gifting) such a beautiful and unique piece of the Earth is sufficiently special that anyone can feel like royalty in the eyes of their loved ones.

So how do gemstones form? And does knowing the origin of gemstones impact the value we assign to them?

Admittedly, gemstones are not my expertise and I have little experience in the field of mineralogy as a whole. Thus I can only comment at an introductory level on the "geology of jewels" and would direct you elsewhere for more detailed discussion. A basic understanding, however, is all that is necessary for this week's post, which stands in response to an article by Dr. Andrew Snelling entitled "Rubies and Sapphires - Sparkling Reminders of God's Judgment." There, Dr. Snelling argues that gemstones formed under the unique geological conditions concomitant with catastrophic processes during and shortly after the global Flood. In other words, they should remind us of a period in Earth history when God's judgment resulted in cosmic overturn. Noting also that sapphires (among other gemstones) are described as construction materials in the New Jerusalem (i.e. heaven; Rev. 21:19-20), he concludes: "[Rubies and sapphires] are not just pretty reminders of God’s creativity, but they serve as eternal reminders of God’s righteousness, judgment, and mercy." I will return to the theological symbology of gemstones, but first want to consider whether Dr. Snelling has provided a plausible mechanism by which gem-quality minerals should be found in such natural abundance.

Formation and occurrence of Himalayan rubies and sapphires

The translucent crystals commonly known as ruby and sapphire are gem-quality variants of the mineral corundum, which is comprised of aluminum (Al) oxide (the chemical formula is Al2O3, though traces of chromium or iron actually give the gem its color). Aluminum is found in common minerals like feldspar and mica, but only as a minor constituent. Under the right conditions, however, aluminum may concentrate to form Al-bearing minerals like corundum. One example, and the major source of industrial aluminum, can be found in many tropical soils (laterites), where rain and groundwater leach water-soluble metals from rocks and soils near the surface. Water-insoluble oxides, such as aluminum and iron oxide, concentrate as residuals in the hard soil horizon and are later mined, refined, and smelted to make cans of Dr. Pepper--well, among other products, but life has priorities.

One could sift through megatons of lateritic soil, however, and never find a corundum gemstone. The formation of ruby and sapphire not only requires the concentration of oxidized aluminum in a fluid phase, but other unique physical conditions--namely, high temperatures and pressures not found in surficial soils. So rubies and sapphires are formed deep beneath the surface of the Earth, under the tremendous weight of overlying sediments, and typically during regional metamorphism in transcompressional tectonic settings (i.e. where mountain chains are forming as tectonic plates collide). Several factors made the Himalayan orogeny an ideal setting for the formation of Al-rich gemstones: 1) it was a broad scale event, resulting from the collision of India with the rest of Asia, in which very high temperatures and pressures dominated; 2) the rocks being metamorphosed were comprised largely of limestone/dolostone, which was deposited on a shallow carbonate platform (like the Bahama Bank), and thus were rich in aluminum but poor in silica--a factor that promoted the localized formation of corundum over aluminosilicates like kyanite and sillimanite; and 3) granitic magma bodies intruded the metamorphosed sediments in several stages, which added heat and pressure to the system while mobilizing aluminum and other ions in the rock. Though I have simplified the "recipe", one can begin to envision the process by which natural gemstones are cooked in Earth's kitchen. But at this point, the recipe I described is missing one vital element, which Dr. Snelling neglected to discuss.

Better set your clocks; this recipe calls for a lot of time.

Deposition of carbonate and evaporitic sediments

Before the collision of the tectonic plates now hosting southeast Asia, the surface of each plate was covered with several miles thickness of sedimentary rock layers. Modern Himalayan mountain peaks are the carbonate, shale, and sandstone remnants of a long and dynamic depositional history, which has been interpreted to reflect environments ranging from carbonate platform and lagoon (coastal) to deep-sea turbidite and flysch (continental slope) settings. While the rate of deposition varied significantly over geologic time, numerous sedimentary layers show evidence of very slow deposition. In particular, organic-rich shales need time to trap organic matter in the water column, which first needs time to grow. The minerals in some Precambrian shale layers also contain geochemical proxies for euxinic conditions, meaning they were deposited in an ocean chemically distinct from that of today. Euxinia refers to a water column that is poor in oxygen but rich in sulfur (like the modern Black Sea), implying that these shales were deposited in deep, stagnant water, which could not have supported complex modern or fossil marine life in the years leading up to the flood (and no, the massive addition of hydrothermal fluids during the Flood would not create such conditions; besides, most Precambrian rocks are interpreted as pre-Flood sediments). Although mudstone can be deposited rapidly under the right conditions, the Precambrian shales of the Himalayas were certainly not.

Another evidence for slow deposition is the shear mass and composition of carbonate rocks in the Himalayas. Dr. Snelling and others may try to argue that carbonate minerals precipitated rapidly from a bicarbonate-saturated slurry under catastrophic conditions, but rapid crystallization always results in the formation of aragonite--not calcite and dolomite, regardless of the magnesium concentration. Diagenetic alteration of aragonite to calcite and dolomite also takes time, which is not available in the Flood model. It is simply unreasonable to think that advancing flood waters deposited alternating layers of specific carbonate lithologies at a rate no less than 50 meters per day, while preserving fossil and geochemical patterns that could be correlated across the entire globe.

Since the purpose of this article was to discuss gemstones, I should note that salts from sedimentary evaporites (like gypsum) played a major part in mobilizing metals (like aluminum) to allow the growth of ruby and sapphire crystals. Young-Earth researchers have elsewhere attempted to explain the unlikely occurence of sedimentary evaporites in a Flood geology model using isolated (and hypothetical) cases-in-point, but the challenge becomes even greater in the context of the Himalayan sequence. In other words, it is hard enough to explain how thick layers of salt can form in under a year; postulating the accumulation of thick layers of salt during catastrophic deposition of 5 miles of sediment in under a year borders on desperation. Even granting the impossible, however, the Himalayan mountain range did not exist before the Flood. So where did it come from?

Himalayan orogeny

Biostratigraphic and radiometric age constraints suggest that sedimentary deposition occured between ~1 billion and 55 million years ago, after which continental collision initiated metamorphism, uplift, and erosion of the sediments. Dr. Snelling rejects this timeline, but it's worth noting that multiple independent methods have been used to detail the structural history of the Himalayas. If uplift began ~55 million years ago, then syntectonic deposits (sedimentary rocks that form in response to the erosion of adjacent mountain ranges) should not yield dates older than 55 Ma (they don't). Radiometric dates of minerals and intrusive magma bodies formed during metamorphism should not be greater than 55 Ma (they aren't), and should get younger away from the center (they do). A reduction in atmospheric carbon dioxide and global temperatures during the later Cenozoic, which is recorded in rocks around the world, has been partially attributed to the induced carbonate weathering of the massive Himalayan range. Oxygen isotopes from fossilized mammal teeth on the Tibetan plateau record a dramatic shift in plant life due to higher elevation, and thus correlate to the inferred multi-million-year uplift history of the range. Numerous, falsifiable predictions originate from the conventional understanding of the Himalayan orogeny, and can be tested by field observations. Can the same be said for the Flood geology model? Dr. Snelling writes:

"Pre-Flood and early Flood sedimentary and igneous rocks were buckled, squeezed, and heated, transforming them into the metamorphic gneisses and granulites that host the ruby and sapphire deposits of eastern Africa, Madagascar, India, and Sri Lanka. Then, according to the biblical model of earth history, when rapid crustal plate movements were quickly slowing down at the end of the Flood, the Indian plate collided with the Eurasian plate to form today’s Himalaya mountains. Limestones that had been deposited early in the Flood were then metamorphosed into the ruby-containing marbles of Myanmar, Vietnam, Nepal, Pakistan, and Afghanistan."

What distinguishes the statement above from a gratuitous assertion? Dr. Snelling is eager to present a simple geological story for his readers--I understand the article is written on a popular level--but employs the technique of "so-so" story telling. In other words, despite his use of scientific terminology, Dr. Snelling's description lacks scientific reasoning--saying it was so does not make it so, and no positive evidence is given for the young-Earth version of the story. Alternatively, abundant evidence against the Flood geology model for the formation of Himalayan gemstones should motivate us to consign Dr. Snelling's summary to the realm of science fiction. To be clear, I am not trying to belittle Dr. Snelling or the scenario he proposes. Rather, I am simply trying to make a categorical distinction between a scientific approach to the problem and simple storytelling. Many conventional geologists have faced similar criticism from their peers, and it's only fair to hold Dr. Snelling equally accountable. Should Dr. Snelling provide falsifiable predictions that stem from the Flood geology model, and then test those predictions with existing geological data, I will gladly retract my criticism.

On a quick side note, I am troubled by the phrase "according to the biblical model of earth history, when rapid crustal plate movements were quickly slowing down..." (emphasis added), particularly since I am unable to find a description of plate tectonic rates in the biblical text. The model of catastrophic plate tectonics offered by young-Earth geologists is not rooted in scripture so much as an admission that the preponderance of geological evidence warrants a belief that the continents have moved thousands of miles over geological history. An a priori reduction of geological history to <10,000 years forces young-Earth geologists to squeeze plate tectonic movements into a year-long catastrophe, however, despite the fact that doing so undermines the evidence for plate tectonic theory. The result is an extravagant geological tale, which has attained the status of dogma among young-Earth researchers and thus can neither be criticized effectively from without nor from within. In the meantime, we'll just have to pretend that it works (though if you're interested, Greg Neyman offers a helpful discussion here that highlights a few problems with catastrophic plate tectonics).

Growth of gemstone-quality minerals: pressure, temperature, and time

Many Himalayan rubies are now hosted in various types of marble. Marble is a metamorphic rock, which formed from carbonate rocks during the mountain-building process. Petrologists can estimate the pressure and temperature at which minerals grew as a result of metamorphism, using various chemical proxies. Rubies in the Himalayan marble formed at temperatures between 620°C and 650°C and pressures between 2.6 kbar and 2.9 kbar (between 2,600 and 2,900 times atmospheric pressure at sea level). Intrusion of granitic plutons during the mid-late Cenozoic influenced the mobilization of aluminum and other metals in hot metamorphic brines (very salty water), which promoted the growth of large, euhedral crystals of corundum.

Dr. Snelling describes the same process and applies it to the year-long Flood scenario without qualification. Several problems exist, however, with regard to the timeline:

1) Rapid crystal growth is possible, but tends to result in lots of tiny, poorly developed crystals (at least outside of a laboratory setting). The abundance of large, well developed gemstones in nature (albeit rare from an economic standpoint) is testimony to a long metamorphic history of the Himalayan mountain range, wherein crystals grew very slowly for hundreds or even millions of years.

2) Mineral growth is limited by the dissolution and transport of key elements to the site of nucleation. Despite high temperatures in the metamorphic system, the diffusion (movement through solid rock) of elements like Al, Cr, Fe, and others is extremely slow in rocks under pressure. By way of comparison, near-surface groundwater in highly permeable aquifers commonly moves only tens of meters per year! The rate of crystal growth also depends on the concentration of elements in the fluid. Given that the necessary components of gemstones exist as trace elements in the host rock/fluid, it is unreasonable to posit the formation of large rubies and sapphires in a matter of days, months, or even a few thousand years.

3) Since aluminum oxides are rather water-insoluble, the volume of metamorphic fluids necessary to promote the growth of gemstones is many times that of the host rock. This process takes far more time (and water, ironically) than is allowed in the Flood scenario.

4) Rubies and sapphires are mined at the surface of the Earth, but are formed many kilometers below your feet. So how do they get from point A to point B? Dr. Snelling proposes that gemstones were carried to the surface by rapidly ascending basaltic magma shortly after the flood. I am unsure, though, how he makes the connection (or why). Rubies can be found in situ within marble now exposed in the mountain peaks. Not only does this make the "basalt express elevator" an unnecessary explanation for the evidence, it also means that several kilometers of sediment have been removed since the formation of these rubies. How long does it take to remove such vast quantities of sediment? The steep slopes of Himalayan peaks suggests that it was far longer than ~4,000 years (i.e. slow removal of hard rock through snow, ice, and gravity; not rapidly from receding flood waters over soft-sediments).

Judgmental gemstones: the theological connection

Previously, I cited Dr. Snelling's description of rubies and sapphires as a reminder of God's moral attributes, since he classifies them as geological products of the Flood. I think that most people (religious or not) can appreciate Dr. Snelling's desire to attribute moral significance to natural wonders. He does not intend to give us a childhood lesson, however, but scientific grounds for using gemstones "as a witnessing tool and as a personal reminder of God’s transforming power on our behalf." Despite his seemingly pure intentions, I wonder how effective a misinformed story of the gem's origin could be. Either the recipient recognizes that the story is contrary to the facts, and assigns a false story to God's message, or the recipient is won over by a bad argument and consequently stands on shaky ground.

But what is wrong with telling the real story? Is God's magnificent masked by a process that is actually far more intricate and complex than the Flood geological scenario? If you can recall the full process by which Himalayan rubies and sapphires were made, consider the range of variables involved: life cycles of marine planktonic organisms, which concentrated organic matter and trace metals in carbonate sands--all of which controlled the metamoprhic fluid chemistry that promoted the growth of gemstones; the ancient sun evaporating excess water in just the right place to precipitate salts necessary to mobilize the elements; precise and timely emplacement of magmatic bodies of the proper composition and viscosity; the plate tectonic movement of massive continents along a 70-million year collision coarse, which made contact at the precise moment in time, and compressed sediments and uplifted mountains at the precise rate. All of these sensitive, geological factors worked in perfect accord to make some of the world's most spectactular minerals, and to make them accessible to human cultures. In the words of N.T. Wright, "Dust we are, and to dust we shall return. But God can do new things with dust." There were, perhaps, a million divine reasons behind the formation of rubies and sapphires, but I propose that we can know at least one: that we might truly understand majesty, and ask rhetorically, "What is man, that you should be mindful of him?"

Foundational gemstones: a heavenly vision

For those not familiar with the vision described in Revelation 21:19-20, sapphires (among other gemstones) are mentioned as construction materials in the New Jerusalem. The broader context of this chapter is responsible for our vision of heaven as a large city with streets of gold, and my impression is that Dr. Snelling (like others at AiG) believes that precious metals and gemstones will actually comprise the base of a structure with dimensions equal to that recorded in John's unveiling. Many years ago, I read arguments by Henry Morris and others that insisted on a consistent "literalist" hermeneutic between Genesis and Revelation--in other words, if we accept Creation/Flood account of Genesis as historical and scientifically descriptive, then we must accept John's vision in the same terms and expect heaven to be made of such Earthly materials in the exact dimensions listed. Granted, the chapters are exegetically linked (the Book of Revelation contains more powerful and obvious intertextual imagery than any other book of the NT), but I now perceive that 'missing the point' in Genesis has led some to 'miss the point' in Revelation.

How so?

If your heavenly vision includes streets of gold and walls lined with precious gems, then I exhort you to open your eyes just a little wider. Take note that John only describes the material nature of the most basic features (walls, streets, etc.), but uses the most beautiful and valuable descriptors to do so. The take home message is that even the simplest, most common features of heaven are worth far more than the most valuable and beautiful features of the world you now know. Let your hermeneutic be as deep as time itself, albeit still faithful to the Word, and you will be rewarded with the majesty of a God that can hardly be captured by words.

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