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The chemical composition of a mineral can be expressed by a formula but said formula might not be exact.  It simply means that this or that named mineral refers to definite limits.  The variation between the two limits is called solid solution.  For example, the glassy, brittle, translucent/transparent mineral known as olivine varies from forsterite which is a pure magnesium silicate, to fayalite, which is a  pure iron silicate.  Both are uncommon but the variations between the two are very common.  There are also tephroite, roepperite,  knebelite, and  monticelllite.   A gem variety of olivine is  peridot, which is green,  and there are green sand beaches in Hawaii.

Posted by oh5/ojhoff at 3:34 PM CDT
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mineralogy ho hum

I've mislaid my mineralogy text and I am postitive that if I have any readers they probably aren't too unhappy.  I know that's some dull reading.  It's more interesting to hear about, for example, scams in the world of colored stones and who got by with what.  All the juicy details.   I am not a  purist but I am upfront about rocks that have been altered, if I know about it.  I wet down a dry slab now and then to show what it will look like polished.  But sometimes I don't.  Depends on what it looks like and how it strikes me.  I was reading about dealers who fiddle with their photos in adobe.  I have done this but not to deceive people.  It is that sometimes I see one thing with the naked eye and another in the photo, and I am trying to make the two match. 

It's a chilly day.  Maybe I should bake.  Grandma used to make oatmeal cookies that she called rocks.   

Posted by oh5/ojhoff at 1:22 PM CDT
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next topic

I don't have access to the mineralogy book I am studying, so I have given some thought to the next topic I might explore.  The word tektites popped into my head.  These are the small bodies of silicate glass that are believed to be of extraterrestrial origin.  Their similarity to terrestrial obsidian caused them to  be referred to as obsidianites.  But more evidence has come in that they did not originate on earth. 

I am photographing, pricing and posting the minerals I got in a trade.  My business is not concentrated on mineral specimens and it moves rather slowly so I think a majority of these will end up in my private collection.  

Fall is in the air, but it's still nice and warm.   

Posted by oh5/ojhoff at 10:19 AM CDT
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There are two series of garnets, the pyralspite and the ugrandite.  Within the two series are three varieties each, for a total of six.  Many individual specimens are a gradient between two types.   All have gemstone potential, are glassy, hard, and transparent to tranlucent.  Garnets come in all colors, includinga  recently discovered blue, but red and green are the most well known.  Garnets were formed under hydrothermal pressure and are found in pegmatities and granites. 


As the birthstone for January, the garnet is the first of my revised and enhanced informational videos I have done and is linked to the front page of my website. 

Posted by oh5/ojhoff at 6:13 PM CDT
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great trade
It has taken me a while to unpack the box I got from someone with whom I made a rock trade.  This person sent me a lot of intriguing stones, some of which I was unfamiliar with.  I was amazed to open a newspaper and napkin packet all done up with masking tape and discover a garnet almost the size of a baseball.  Plus two other garnets including one from Norway.  My next chapter in the mineralogy book deals with the garnet group of silicates so that works in well.  Was also pleased with a whale bone fossil from the Miocene and  specimen that includes both gold and silver, plus iron pyrite.  And, oh yes,  bluish  kyanite.   Samples too numerous to mention here.

Posted by oh5/ojhoff at 4:26 PM CDT
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The epidote group of minerals includes epidote, zoisite, clinozoisite, and piedmontite.  I always regarded epidote as ugly but perhaps I was thinking of massive epidote.  I did find a specimen in my grandfather's collection that was the text book pistachio green and very attractive.  Zoisite comes in many colors.  The pink variety is called thulite and is glass and gem-like.  I am not familiar with the other two minerals.  All are found in metamorphic rocks.

Posted by oh5/ojhoff at 12:08 AM CDT
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mineral specimens

I just did a rock trade, my first in years.  A gentleman sent me mineral specimens and I am getting a box of stone tools and Minnesota materials ready to send in return.  My rock business is perking along in spite of the economy.  It's a low cost, wholesome activity that families can enjoy.  The temps are cool this summer so I suppose we'll have an early frost. 

Silicates are a huge group of minerals composed of silicon, oxygen and one or more metal.  Quartz is both a silicate and an oxide, but when it's included as a silicate, basically most of the earth's crust is composed of silicates.  Silicates are hard to identify because of their chemical complexity but most are glassy, transparent or translucent, and very hard.  They are classified in many groups.  The zirconium group consists of zircon, a gemstone, and thorite.

 Zircon occurs worldwide and can be found in many colors.  It has an unfair reputation as an imitation diamond.  Thorite is not as hard and is quite rare.  It often contains uranium and is radioactive.

Posted by oh5/ojhoff at 10:29 AM CDT
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I spent all day at the church helping with a bluegrass festival.  The less said about that, the better.  I donated a rock collection to the silent auction.  My suggested starting bid was $40.  Two kids started at bidding war and their first offer was $2.  They got it up to $10.  I let it go at that. 

 I put in the winning bid on a signed painting.  The artist had won first place on another painting at the Colorado State fair.  This one didn't do much for me but I figured it must be good so it will make me look a bit more cultured to people who know about such things.  Or else it's like the emporer's new clothes.  I got a book on making the flat breads of many cultures, and a CD telling the story of the japanese girl who made the thousand cranes, narrated by Liv Ulman. 

I have some rock orders to ship out  in the next couple of days and others pending.  Enough to keep me busy. 

Posted by oh5/ojhoff at 5:39 PM CDT
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this summer

I have joined some lapidary, crystal and geology groups at social networking sites such as facebook, myspace, cafemom, yahoo, flickr, and so on.  Have been researching old pics from the early days of the rock business which included more field trips and photos, albeit not very sharp ones, of formations and mountains and so on.  I've run into a few good ones, of Mount Ranier and Mount Baker, and one of my grandfather in his shop standing in front of a poster size image of Einstein, whom he admired greatly. 

I did some rock painting and distributed a couple of the sandstone slabs to other artists to see what they could do with them.   

Posted by oh5/ojhoff at 10:25 AM CDT
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It just occurred to me...I have been blogging about mineralogy, and studying it while I ago, and I didn't have a workable cohesive definition of mineralogy in my head, beyond the obviouis which is the study of minerals.  SO I decided to Google it, and to access the wikipedia. 

To make a long story short, mineralogy has been a field of study since  the time of the ancient Greeks, Aristotle on through Pliny the Elder, and at the same time, in another part of the world, the Chinese from the time of the  Han dynasty and before that, were studying minerals and coming to the same conclusions as the philosophers of the ancient Babylonian and Greco-Roman civilizations, albeit with a Taoist view.  

Early considerations of mineralogy included speculations on their metaphysical properties (sound familiar?).  The father of modern mineralogy was the German Agricola   The invention of the microscope pushed the science forward a great deal.

In modern times there are several branches of mineralogy:   physical, chemical, optical, crystal structure, bio, formation habit, use of minerals, and descriptive, the category into which I feel the book I am reading falls.

Posted by oh5/ojhoff at 10:08 AM CDT
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rock painting

I joined two yahoo rock painting groups but I haven't done any painting.  Yet.  Today I prepared the surface of a sandstone piece, of which I have several.  I might saw off the bottoms so that they stand on a level surface and paint a few, and give away or sell the ones I can't use. 

 Borates are a class of minerals that combine boron and oxygen in combination with a metal.  There are 45 of them but the book I am reading describes only five of the most common.  Borax is the best known.  It appears in the dry beds of salt lakes.  It is soluble in water.  Colemanite looks similar but is only soluble in hot hydrochloric acid.  Boracite is found in salt domes in Louisiana and also in Europe.  It is quite hard.  Sussexite is manganese magnesium borate.  It is brittle and forms as fibrous veinlets or in grandular masses.

 By far the most interesting is ulexite.  We used to call it TV rock.  Its radiating needle shaped crystals bring an image from the bottom right up to the top, like a magnifying glass (almost).  Kids like it.  So do I.  

Posted by oh5/ojhoff at 5:27 PM CDT
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Yesterday at B Dalton I saw the neatest book....The Rockpicker's Guide to the North Shore, or something like that.  I didnt have time to browse through it but I do think that's a book I want to own.

 A nice day.  The first one in ages.  I have to take some photos for a potential customer, and plant my herbs.  As I mentioned, the rock business sucks so I might put it on the back burner and concentrate on writing for a time.  But I will probably end up writing about rocks :)

Posted by oh5/ojhoff at 11:35 AM CDT
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ho hum

Rock business sucks.  No wonder.  People are selling their belongings to pay bills for food, gas, and so on.  And who would have thought we'd get three blizzards in two weeks?

 The brucite group of oxides are structures of manganese and magnesium.  Their structure is the layer type.  In the mineral brucite, the layers are easily separated.  Pyrochroite is similar to brucite but it weathers more easily.  Both are very soft.

 Limonite is a mixture of minerals and is an important ore of iron in some places.  Psilomelane is a weathering product of carbonates and silicates and is a manganese mineral.  Gummite is also a mixture of minerals, mostly uranium, lead and thorium.

Posted by oh5/ojhoff at 10:17 AM CDT
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stone tools
Sometimes I get tired of the same old stuff.  I decided to photograph stone tools.  Interesting huh?  I have a bucket of them given to me by a neighbor who had collected them throughout the years, here in Minnesota and elsewhere.  That was before the days of archaeology, so I have no idea of the locale or circumstances they were found in.  Most are skin scrapers.  The arrowheads tend to be fragments.  I have posted about ten on my Whats New page so far.

Posted by oh5/ojhoff at 8:02 AM CDT
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what next?

Have I learned enough about mineralogy?  Probably not, but I need to think ahead about what I am going to read/write here next.  I am thinking in terms of earth science, paleontology, or gemology.  Dinosaurs?  Growing crystals?  Lapidary?

Speaking of which, I have several tumblers going, and the vibrolap.  A man who attended the dance in our barn has installation of rock saws as a career and he said the blade on the 24 inch saw is probably worn out and that is why it doesnt work.  He has promised, if he can find out the arbor size, to find a second hand  or at least a reasonably priced blade.  Lucky break. 

Posted by oh5/ojhoff at 12:23 PM CDT
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flint knappers

I had visitors to the shop yesterday.  Their purchase was small but I didn't care because they were an interesting couple.  They were finding materials to do flint knapping.  Lots of times archaeologists will make tools so that they have an understanding of the process and can recognize a tool when they see it in the field.  An archaeologist who drops in now and then told me how he was teaching a tool making class.  One could do the same with jewelry I suppose...attempt to make jewelry in an ancient style using the technology that would have been available. 

 I am photographing stone tools, mostly skin scrapers.  The ones that are intact I will offer for sale.  The fragments may be useful to a class for study.

Posted by oh5/ojhoff at 3:10 PM CDT
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The diaspore group includes minerals that are important sources of metals.  Diaspore is a major constituent of bauxites.  Goethite is formed from weathering of iron bearing minerals.  Bauxite is the major ore of aluminum, and manganite is a minor ore of manganese.  The only one of these that I may possess somewhere in my collection is goethite. 

I have been experimenting with a photo program, hoping to come up with an image from which I could paint a rock, mineral or crystal.

 Nice day today.  For the first time I think I can go out and work in my shop.

Posted by oh5/ojhoff at 10:44 AM CDT
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uraninite group of oxides

The uraninite group consists of uraninite, which is the major ore of uranium, and thorianite, the major ore of thorium.  These two are on a continuum in their structure and many intermediate minerals are possible.  Not sure if any of them are named. 

On the same page in the text I am reading is chrysoberyl, which does not belong to the group but is a curiosity in the world of minerals.  Chrysoberyl includes two gem varieties, cats-eye and alexandrite.  Their hardness on the Mohs scale is 8.5

 A dance will take place here in the barn on Friday evening.  A local charter school has an artist in residence, a dance instructor, and they are all coming to practice what he has taught them this week.

Posted by oh5/ojhoff at 6:11 PM CDT
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I have seen a lot of rocks, minerals, crystals and so on in my lifetime.  I will confess I've never thought much about rutile except as in rutilated quartz, and I thought it was a word to describe a needle shaped formation.  In reality it's a group of oxides of which the mineral rutile is a member.  I guess I did know that but I still thought of it was needle shaped.

 Rutile the mineral is common and widespread but only in small amounts.  Resistant to weather, it is found very often in sediments.  The crystals are clear, and have been synthesized.  Other minerals in the group are pyrolusite, cassiterite (an ore of tin) and plattnerite.  The only one of these that I am majorly famiiar with is pyrolusite.

Posted by oh5/ojhoff at 9:16 PM CDT
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Spinel is the most complex group of oxides.  It includes both natural species and many synthesized compounds.  Gem quality natural stones are found in many locations, and synthesized stones are fairly inexpensive.  Aside from the mineral spinel, there is gahnite which forms in silica rich granite pegmatities, hercynite, a comparatively rare mineral which has been found in diamond placers, magnetite which is an important iron ore and the most magnetized of all minerals, chromite, the ore of chromium which is only weakly magnetic, and hausmanite, which occurs with manganese minerals in veins and metamorphic rocks.  There are also some other lesser known spinels, some of which have been synthesized and it's not known if they occur naturally anywhere.

 I am really way too tired to care much about this but I do appreciate the good quality and very cheap spinel as jewelry stones.

Posted by oh5/ojhoff at 6:31 PM CDT
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