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01/15/09
serpentine group

The serpentine group of sheet silicates is called that because most of the examples have a green, patterned appearance.  The recognized varieties are antigorite, lizardite, and chrysotile.  It is very difficult to tell them apart without using x-ray and miscroscope equipment.

 It is not known why the serpentine varieties differ in appearance.  Reasons may be impurities, pressure and temperature when they were formed, minerals present, the water content, and so on.

Fibrous serpentine is used to make asbestos fabric and making fire brick.


Posted by oh5/ojhoff at 1:00 PM CST
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01/14/09

http://www.oliviahoff.com



Posted by oh5/ojhoff at 9:43 PM CST
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01/12/09
sheet silicates

Sheet silicates exhibit one directional cleavage.  This is because the bonding between the sheets is weak.  These minerals have a greasy feel and lubicating qualities.  An example of weak bonding is mica,in which the sheets separate easily.

 The kaolinite group includes kaolinite and three others with similar chemical composition but different structure.  The other three are dickite (funny name) , nacrite, and halloysite.  Kaolinite is important for use in pharmaceuticals, firebrick, china, and as a whitening agent.

I joined an online wire wrap group today.  I wonder if I will learn anything.

 

 


Posted by oh5/ojhoff at 10:37 PM CST
Updated: 01/15/09 12:42 PM CST
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01/06/09
double chain silicates

The double chain silicates are formed so that many ionic substitutions are possible, therefore the chemical varieties are endless.  All double chain silicates are in the amphibole group.  These contain water and are formed at lower temperatures than olivines and pyroxenes.  There are over thirty varieties.  Some of the more well known are actinolite, of which nephrite jade is largely composed, and hornblende, found in basaltic lavas in mountainous areas of the world.  Some very large rocks are mostly hornblende. 

 A bit warmer today.  I may get back to the photographing of materials from Ely or whatever I can find.


Posted by oh5/ojhoff at 11:11 AM CST
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12/28/08
the bad month of December

Between being sick, and snowed in, I've barely let the house this month.  Now I have to venture out and fill a rock order.  Fortunately, my worst cold in years might be going the other way.  On the dark side, it was thirty below this morning. 

The next group of minerals to be considered are the single chain silicates, also known as pyroxenes.  This group includes several well known gemstones. 

 Here are some of the single chain silicates:  diopside, enstatite, hedbergite, aigote. ju[ersthene, aegerite, johannsenite, rhodonite, jadeite, wollastonite, spodumene, chrysocolla.  How many do you recognize?Quite a few, I would imagine.  This is a major group of rock forming minerals.


Posted by oh5/ojhoff at 10:10 AM CST
Updated: 12/28/08 10:22 AM CST
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11/29/08
Christmas shoppin

Christmas is not a big season for my rock business.  It seems such a short time ago I was making this same remark :)  A few days ago I went with my brother to the science center and retrieved our fluorescents and made brave promises to get involved in the center as far as earth sciences are concerned.  Then we had a handful of charter school students visit and showed them the rock equipment and explained a few of the processes we are able to do.  It was, unfortunately, the coldest day of the year thus far.  I still have hopes of making plaster casts of fossils and of growing crystals so I can provide a more interesting hands on experience for such groups in the future.

 The season of peace and good will and good cheer isn't starting out all that well.  A gun battle in India, overzealous bargain hunters trample a store worker to death, shots fired in a toy store....

Maybe Im stupid but I still think most people are good.  Let's try to make a better world. 

 

 


Posted by oh5/ojhoff at 10:39 AM CST
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11/07/08
ring silicates

The ring silicates are complex in structure.  I struggle to understand them and wouldnt begin to try an explanation.  But the minerals that fall under this category are well known for their beauty:  tourmaline and beryl. 

 Tourmalines are found in pegmatites and are often treasured as gemstones, in particular the ones of which the chemical structure has changed during the formation, resulting in many colors.  I sold green tourmaline points in my shop for a while and they were tremendously popular.

Beryl in its transparent form is highly valued as emerald, aquamarine, and heliodor.  Its typical crystal form is a six sided prism.

Cordierite has the same structure as beryl but a different chemical composition.  It resembles quartz.  It doesn't fracture easily during heating and cooling and is therefore valuable as a refractory.

 Miserable cold and rainy today.  


Posted by oh5/ojhoff at 10:40 AM CST
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10/28/08
weather....

The wind was brutally cold on Sunday.  Two parties in the barn were not held..on cancelled and the other postponed.  The house is cold.  A decision has been made to hold off on using electricity or propane for heat until Nov. 20.  Of course, that means a fire in the furnace which sometimes doesn't happen.  

As their name implies, the double tetrahedral silicates are complex in structure.  The melllilite group includes gehlenite, akermanite, and hardystonite.  All are commonly found in limestone.  Akermanite is relatively rare in nature but is found in industrial slag.  Hardystonite has been found only in Franklin, NJ.  All are dull in sppearance and to be honest, I have never knowingly seen any of them, nor do I care to.


Posted by oh5/ojhoff at 12:19 PM CDT
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10/09/08
subsaturate silicates

The easiest way to sum up the chemical composition of the subsaturate group is to say these have extra oxygen ions.  Examples are kyanite, staurolite, sillimanite, andalusite, and topaz.   I just recently acquired a sample of the kyanite and found it attractive with its underlying blue shimmer.  My specimen comes from North Carolina.  Staurolite is found in a range from New England to Georgia, also in Sweden, and often forms cruciform crystals that can be made into cross jewelry.  Sillimanite has the same composition as kyanite but a different structure and is a bit harder.  Andalusite also has the same chemical composition as kyanite and sillimanite.  It forms at lower temps and is sometimes faceted and used as a gem.  Everyone knows topaz.  It has a similar structure to other subsaturates but is otherwise unrelated.  Topaz can be found in a variety of colors.  The amber colored is the birthstone for November.


Posted by oh5/ojhoff at 2:46 PM CDT
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09/23/08
olivines
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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09/15/08
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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08/29/08
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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08/22/08
garnets

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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08/19/08
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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08/15/08
epidote
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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08/11/08
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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07/14/08
yesterday

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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06/26/08
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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05/29/08
mineralogy

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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05/07/08
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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