Popular Mineralogy

Popular Mineralogy Fascinating mineralogy and earth science for the amateur mineralogist and serious collector - #42

______Seeing Inside Minerals by Andrew A. Sicree, Ph.D. ______

Discovering X-rays but only a shadow of the skin and muscles: the first medical X-ray All mineral collectors know image. Roentgen’s X-rays were a about X-rays and most of us have fantastic boon to medicine enabling heard that they are useful in doctors to “see” broken bones identifying minerals. But the details inside their patients. In some are a bit sketchy. What are X-rays? countries, X-rays are called And how do they help us identify “Roentgen rays” in his honor. minerals? Making X-rays Wilhelm Roentgen is usually credited with the discovery of X- X-rays are generated when a rays for his work in 1895. high-energy beam of electrons Although the claim that Roentgen (usually inside of an evacuated was the first discoverer of X-rays is tube) hits a target (usually a metal somewhat debatable – there were such as copper). Electrons others who observed the effects of belonging to atoms in the target are X-rays earlier – certainly Roentgen knocked out of their orbits by the was the first to extensively study electron beam, and when they the properties of X-rays. While return to their original orbits, the working in the dark in his lab with a atoms release energy, usually in the cathode-ray tube, Roentgen noticed form of x-rays. that a nearby screen covered with X-rays are, quite simply, a form barium platinocyanide (doesn’t of “invisible” light, which is to say everyone have one of these in his that they behave like visible light. lab?) was glowing or fluorescing, Like visible light, X-rays have even though it was well beyond the wave-like behavior and thus one range of any electrons from his can measure their wavelengths. cathode-ray tube. The difference between x-rays and Experimenting further, Roentgen visible light can be found in their decided that he had discovered a wavelengths. Visible light new and different form of radiation, wavelengths fall in the range of which he labeled X-radiation, about 700 to 400 nm (nanometers, signifying its unknown nature. He equal to one billionth of a meter). determined that X-rays could Below 400 nm is the ultraviolet penetrate opaque matter, passing (UV) region. Shortwave UV lamps through paper, wood, skin, and even favored by mineral collectors put thin sheets of metal. This led to the out light of about 253 nm. X-rays famous photograph he took of a are much shorter than UV, having woman’s hand – which clearly wavelengths in the 10 to 0.01 nm shows the bones of the hand and range. In other words X-ray waves even a ring on one of the fingers, are about one-hundredth to one-

©2011, Andrew A. Sicree, Ph.D., [email protected] ~ 8-11-1 ~ Please do not reproduce or extract without permission hundred-thousandth the “size” of visible light. Access to X-ray apparatus Identification of Costly X-ray diffraction minerals equipment is well beyond the It is precisely these short wallets of most collectors. An wavelengths that make X-rays assortment of X-ray apparatus finds useful in mineralogy. All minerals use by professional mineralogists. are crystalline (even if they don’t Some units analyze single crystals – display good crystal faces) which a small (approximately 1-2 mm) means that their atoms are arranged crystal may be all that is needed. in regular, repeating arrays. The Single crystal diffractometers are wavelengths of X-rays are similar particularly useful when studying to the distances between atoms in a crystals of newly discovered crystal. This allows X-rays to mineral species, but few labs have penetrate crystals. But as X-rays these machines. For identification pass through a crystal, some of the of known minerals, powder X-ray X-rays are bent or “diffracted” by diffraction is quicker and cheaper. the atoms in the crystal. These X- Here a pea-sized grain of a mineral rays will exit the crystal in a must be crushed to a powder (thus different direction than the you have to be willing to sacrifice incoming X-rays. These diffracted some of your specimen). This X-rays produce a pattern dependent powder is then hit with X-rays to upon the mineral’s crystal structure. produce a “powder diffraction Because each mineral species has a pattern” which can be compared different arrangement of atoms in with libraries or databases of its crystals, each mineral will patterns for all known minerals. produce a different X-ray pattern. Unfortunately, X-ray equipment Patterns for most minerals and a is very expensive to buy and to great number of synthetic crystals maintain, so it isn’t something have been determined and you’ll find in the average published in libraries of X-ray rockhound’s toolkit. But prices are patterns. Thus, the X-ray pattern dropping somewhat. The least of an unknown substance can be expensive machines are the new compared with and matched to a “desktop” powder X-ray diffraction specific mineral, yielding the equipment that recently hit the unknown’s identity. This only market – they start at about works, of course, if the unknown in US$50,000. To operate X-ray- question is a previously discovered generating equipment, you must be mineral. trained and licensed by the state. If your unknown is a new One alternative to owning and mineral, the X-ray pattern is still operating your own X-ray extremely useful because it gives equipment is to ship your unknown information about the crystal samples to a commercial analytical system, the size and structure of the lab. They’ll do the X-ray work for crystal’s unit cell, and other useful you for a price. Fees usually range parameters. The X-ray pattern is an from about US$100 to US$200 per important part of the description of sample depending upon the amount a new mineral species. of sample prep needed and whether

©2011, Andrew A. Sicree, Ph.D., [email protected] ~ 8-11-2 ~ Please do not reproduce or extract without permission or not you want a full-fledged Moon could be crawling with the report written or only the raw data stuff. returned. Another extreme rarity is ©2011, Andrew ernstburkeite, a trigonal magnesium A. Sicree, Ph.D. methane sulfonate hydrate, ______Mg(CH3SO3) 2·12H2O. Although this compound is known synthetically (i.e., it can be made in The Rarest a lab), it has only been found in nature in Antarctica. It was found of as a small (0.005 mm) inclusion in an ice core taken from a depth of Minerals 577 m below the Dome Fuji Base on the East Dronning Maud Plateau More than 4400 mineral species in East Antarctica. Not exactly the are found in nature. Some mineral site of you next field trip! collectors are species collectors It is interesting to note that rarity who try to build a collection with as does not always create value. You many of these species as possible. may have the world’s largest It is safe to say that no one has ever specimen of “whatchamaycallitite” collected every known mineral, nor a 1 mm-long beauty of a species does any museum have a complete which is known from only five collection. New species are found almost microscopic crystals found and described each year and many in one locality (which just happens mineral species are quite rare. to be in your backyard). But Many of these species are known chances are good that you won’t be only from a few “spots on rocks” at able to sell that specimen for their discovery site – usually anywhere near the price of a modest referred to as the “type locality”. 1-cm rhodochrosite from the Sweet What is the rarest mineral of all? Home Mine, Colorado. Many candidates could be ©2011, Andrew A. Sicree, Ph.D. submitted for this honor. For some ______rare species, rarity is really a Dr. Andrew A. Sicree is a professional mineralogist function of the inaccessibility of the and geochemist residing in Boalsburg, PA. This Popular Mineralogy newsletter supplement may not collecting site. Tranquillityite, from be copied in part or full without express permission of the Mare Tranquillitatis (Sea of Andrew Sicree. Popular Mineralogy newsletter supplements are available on a subscription basis to Tranquillity) on the Moon is help mineral clubs produce better newsletters. Write undoubtedly one of the rarest of all to Andrew A. Sicree, Ph.D., P. O. Box 10664, State College PA 16805, or call (814) 867-6263 or email minerals. It is a dark red-brown [email protected] for more info. ______hexagonal mineral with the ______interesting formula (Fe2+,Ca)

8(Zr,Y)2Ti3(SiO4)3O4, but it is its origin more than the structure that Inter-Galactic makes it rare. Apollo astronauts collected it and it is unlikely that Diamonds any additional samples will be Diamonds may be a girl’s best collected soon. Whether or not it is friend, but would your fiancée truly rare on the Moon is a separate accept a black diamond in her question – for all we known the engagement ring? We are not

©2011, Andrew A. Sicree, Ph.D., [email protected] ~ 8-11-3 ~ Please do not reproduce or extract without permission talking about clear black like a nice found with kimberlite, the host rock faceted smoky quartz, either. of most diamonds. Geologists are Would she want a diamond that was uncertain of the origin of black, opaque, and looked like carbonados. Some researchers intergalactic space grunge? contend that these stones originated Not all diamonds are transparent in outer space and fell to Earth as a and many that come out of the giant meteoroid about 2.3 billion diamond mines are less gemmy years ago at a time when Africa and than those you see in the jeweler’s South America were joined in a shop. These lower quality single supercontinent. diamonds are sold as abrasives, but ©2011, Andrew A. Sicree, Ph.D. ______most mines make the bulk of their ______profits from the gemstone diamonds they produce. However, in Brazil Mine Shaft and the Central African Republic, there are diamond-mining operations that only produce black Humor diamonds known as carbonados. Question: What do you call 57 politicians at the bottom of an old Carbonado is a variety of abandoned mine shaft? diamond that is black or dark gray. Carbonados are Answer: A good start! adamantine in luster (i.e., they are shiny) and opaque. Unlike most diamonds, they are not single crystals, but rather are polycrystalline, composed of many small crystals. Their polycrystalline nature makes them more porous than other diamonds and also tougher. Toughness is resistance to breakage unlike hardness, which is resistance to scratching (carbonados are about the same hardness – 10 on the Mohs scale – as all other diamonds). Carbonados can and have been cut as gemstones, in spite of their lack of transparency – but they do not take a polish as good as more normal diamonds. Carbonados come from sedimentary deposits in Brazil and the Central African Republic, on opposite sides of the Atlantic Ocean. They are not associated with normal diamonds nor are they

©2011, Andrew A. Sicree, Ph.D., [email protected] ~ 8-11-4 ~ Please do not reproduce or extract without permission Crystal Matrix Crossword Se and Sn ACROSS 1 a flat rock 5 pass in the mountains 8 California pegmatite mine 12 ecclesiastical (ab) 13 ____ tree that yields caucho 14 found in goethite, magnetite, etc. 15 overhanging carbonate formation 18 Russian religious art, often with Au 19 found in smithsonite 20 what some Malays do 22 oxygen, peroxide, etc. 28 found on my knee 30 meaning “and” in Latin 31 Scarlet friend 32 and others (ab) 35 long ___ in the Precambrian 37 __ be or not __ be

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©2011, Andrew A. Sicree, Ph.D., [email protected] ~ 8-11-5 ~ Please do not reproduce or extract without permission 38 animal unchanged by 39 Old Testament (init) A M O K O X I D AN T S millions of years 41 where it’s __ B A N J O E T RH E T A O A G O E R G T O 40 the (Span. fem. sing.) 43 acid in vinegar C R O C L A P EA R L 41 of great price; a gem 45 puzzle creator (init) K I T K A I T E NC A A but 46 how we get club A V L A TE C A S S I T E R I T E not a stone officers K A M E N E C T I D E 44 NiTeSe 50 argon S L U G E X T EC H O 47 basketball 51 Cornwall miners term monopolists for 48 mikes and projectors wolframite 49 ___ Mesozoic, last 52 atomic mass unit dinos 53 Society of Economic 51 tin oxide Geologists (ab) 56 glacially-formed hill 54 oil-state state 57 computer maker 55 Old English letter 58 due to the moon and 56 Kansas sun 59 means “dawn” – early 60 chunk of metal in 61 exterior (ab) geological time 62 found in the Grand Canyon

DOWN 1 not found in selenite 2 landing craft (pl.) LAST MONTH’S SOLUTION: 3 taking ____ A L P S T A U TA L C 4 miner’s term for ZnS L I L T H A N AR E A F L U O R E S C E NC E 5 phosphate deposit T R O T R E 6 alcohol (ab) O B O E A M A L GA M S 7 silver and gold R O C K P T EN O W B O R A T E E X ED R A telluride E L A N V A E R A L 8 a mine D A T O L I T E KA Y E 9 Car 54, Where ___ I N M E AD You? C H A L C O P Y R I T E A C I D E A T S T A N 10 he (pl.) A C M E D R Y TE S T 11 andesite (ab.) 16 not hi 17 state west of Ohio 20 taken ____ 21 natives of New Zealand 23 rare noble gas 24 silver sulfide 25 New Hampshire

26 four THIS MONTH’S SOLUTION: 27 woman’s cloak Mineral 29 Officer of the Guard S L A B G A P PA L A (ab) E C C L U L E I R O N 34 a green mineral S T A L A C T I TE S I C O N Z N 36 recipe (ab)