rock record

The rock record of depositions from weathering is well exposed in southern Minnesota.  There are many sandstone formations, along with some shales, named after area towns.  The Mt. Simon sandstone has rounded sands which indicate high energy deposition, strong waves and currents.  The material contains quite a few brachiopods.

The Hinckley Formation is similar to the Mt. Simon but the latter contains more feldspar.  The Eau Claire Formation is fine grained, suggesting that it was formed under quiet, calm conditions.  

Galesville Sandstone is coarse grained, likely formed under high energy conditions near the shore or beach.  The Ironton Formation contains silt as well as quartz and rests on the Galesville Sandstone, suggesting perhaps that the sea withdrew and redeposition under calmer conditions ensued.

The Franconia Formation is characterized by abundant glauconite, which forms on the sea floor under oxygen poor conditions.  The Saint Lawrence Formation is characterized by carbonates but also contains silt, clay, and sand which indicate fluctuating conditions.  Jordan Sandstone is coarse-grained and contains pebbles, indicating it was formed near a shore or beach.  These formations are interesting as a record of the seas that once covered Minnesota.

Sweltering here a couple of days ago, but now it's cool and almost like fall.

Post pre-cambrian
The post pre-cambrian time in earth's history is the span of years that ranged from 600 to 2 million years ago.  The most notable aspect of this period is that shallow seas covered much of the north American continent, seas that would encroach and then recede.  These seas were different from earlier ones in that they were home to plants and animals.  Each time the seas would spread across the land it would bring with it a new mixture of plant and animal types.  Some of the animals developed hard shells and skeletons which today are found in the various sediment layers left behind when the seas subsided.  It is thought that these skeletons and shells were developed to protect creatures from ultraviolet radiation, from the stress of waves and currents, and from predator stress that occurred in more crowded ecological niches such as near the shores.  Minnesota wasn't as cold during most of this time period.  These marine environments were tropical to subtropical and contained corals as evidenced by the fossils. 

late precambrian
The late precambrian is like a puzzle.  There are difficulties in determining ages of things and sequences of events due to the fact that without fossils, its impossible in most cases to do radiocarbon dating.  There are, however, three distinct ages of rocks.  The oldest are quartz sands, which suggest a widespread sea.  Then the volcanic rocks, the time period during which escaping gasses formed bubbles in which the now highly desirable Minnesota agates and thomsonites were formed.  After that came a period of erosion and sedimentary deposition of sandstones.  The area known as the Duluth Complex (because it is so complex) has many colorful minerals that sound like they would be of interest to the collector.  I don't know if there are any collecting areas there, though.

rock shop cleaning

No time or energy to read up on geology.  We are expecting 300 barn guests and I want to have my shop looking decent in case some decide to visit it.  I really could use a lot more inventory.  When I rearrange things, blank spots appear.  Today somebody visited my shop, a fine person I am sure, but he had a forceful way of asking questions, and I was at a disadvantage because I wasn't expecting it.  Anyway, he asked how long I had lived on the property and I said all my life.  He responded by speculating on how long a life I had lived, and he guessed accurately, which made me damn $%^&**ing mad.  I'm used to people either underestimating my age or holding their tongue.  Maybe time has caught up with me, or I have to get back on the treadmill, comb my hair when I get up, and wear make up not just for special occasions anymore.  !@#$$%^^&&

I made a good trade the other day, jasper and hematite for copper and turquoise and similar ores including lead silver.  

What's new?

I haven't done any research I can blog about, unless I count a couple of articles sold to Mechanical Turk that were based on earlier research.  I wrote about carnelian and crystalline quartz.  I have a facebook page for my business now, and quite a few fans.  I sorted through the newly opened small tumblers again, but a lot of that stuff has to go back in the polish.  As usual, some were gorgeous and some are pretty rough.

 If anybody at all is reading this blog, check out Hoffs Rock Shop on Facebook.  I post different pictures than the ones on my site.

The Middle Cambrian

The Middle Cambrian is what we call the time period from 2500 to 1600 million years ago.  It is important to the economic history of Minnesota, and to the development of this nation as an industrial giant.  Why?  Well, sometime during this era, the atmosphere changed from one rich in carbon dioxide to an atmosphere rich in oxygen.  This happened because of the development of colonies of green marine plants.  The oxygen released iron in the underlying rocks and deposited it as hematite (iron ore), which makes up the iron ranges in Minnesota.  This happened world wide.  The iron ranges on other continents have been determined, by geochronologists, to be the same age.  Other interesting geological events happened in Minnesota around this time, including some mountain building, but this one was probably the most spectacular. 

 I opened up the small tumblers and found some nice Minnesota agates and other agate, jasper and quartz material.  Also, I ordered tumbled rocks, to get more variety and to start making sure I have reasonably priced examples of all the birthstones.  I started with January, and ordered garnet and rose quartz.  Then put the rocks that needed more polish back in the tripoli powder.  I still don't have road signs but I'm carrying on as if I did :)

my shop

My shop still exists both online and in real space but I am not in a mood to blog about mineralogy, paleontology, geology, metaphysics, stone healing, or anything like that.  Two events have happened that have ground my business to a halt.  It was barely chugging along as it was.  I really can't afford to replace the road signs that were taken down.  But even if I do, my inventory is mediocre, leading me to ask myself, why replace the signs?  My cash flow problem prevents me from purchasing fill-in inventory for making my shop look more inviting and colorful and interesting.  There are other ways to obtain inventory.  Self collecting in the field.  Trading with someone who stops in, or by mail.  Processing raw materials on hand to make something new and different.  None of these are as easy as putting in an order.

I have a pile of rocks that I can't do much with, so little by little I am painting on them.  A native American artist stopped in the other day.  He makes sculptures out of rock of all sizes from boulders to small hand sized pieces.  I might not be able to do that but maybe I can make something.  

http://www.oliviahoff.com

andesite
I think I will blog now and then about rocks as opposed to minerals.  Rocks are aggregates of minerals, classified according to how they were formed (igneous, sedimentary, metamorphic).  These can be subdivided into other classifications, such as particle size.  Formation of rocks is a gradual process and one type sort of morphs into another.  Selecting reference points is  arbitrary; however, it has been done and there are a finite number of rock types, according to petrologists.  Usually in books, igneous rocks are considered first.  The first one on that list is andesite, named for the Andes mountains.  It is an intermediate crystalline rock, consisting mainly of plagioclase feldspar.  There is also a mineral called andesite, which confuses matters.

Minnesota precambrian
Ok, now I'm blogging about Minnesota geology.  There is an ongoing search for the original granitic crust, which is elusive.  It is possible it doesn't exist anymore.  It may have been eroded and recycled.  It's also possible that the original crust was basaltic.  One of the difficulties is that most of Minnesota is covered with glacial drift. The Canadian shield contains many belts of volcanic and  sedimentary rock.  It has been suggested that the belts are the uplifted remnants of the "basement", the structure upon which the volcanic-sedimentary features were built.  But that doesn't mean they are the original crust.
It is likely that the very early days of Minnesota were ones of violent volcanic activit

chromates and so on

Chromates are a source of chromium for electroplating steel, and are also used to make stainless steel.  The most popular is crocoite which forms bright, attractive crystals of red, yellow and orange.  Unlike tarapacaite and lopezite, crocoite is not soluble in water.  

Tungstates and molybdates are always associated.  They are important to industry as filaments in bulbs and tubes, and useful in nuclear reactors, to clad fuel rods.  There are three main groups:  wolframite, scheelite, and wulfenite.  The only one that I am personally familiar with as a mineral is wulfenite.  

I am finished with mineralogy for a long while.

 

 

http://www.oliviahoff.com

pyromorphite and others

Pyromorphite is a pseudomorph after galena and cerussite and takes the form of these minerals which it replaces.  It is found in association with lead. 

The phosphate called vanadinite is formed by water which alters the lead ore.  I do have a very nice sample of this somewhere in my collection.  The crystals can be many colors, usually a cinnamon brown.  As far as lead is concerned, vanadinite can be found in commercially viable amounts.  Torbernite is hydrous copper uranium phosphate, and autunite is hydrous calcium uranium phosphate.  The two occur together.  Torberite is bright green.  Autunite is greenish or yellowish and is vividly fluorescent.  

And so I've come to the end of the phosphates.  Next I will dispose of the chromates.  When will I get around to collecting all of these?  Should I blog about rocks next, as opposed to minerals?

 

http://www.oliviahoff.com

very close to the end of mineralogy

Carnotite is an ore of uranium.  It is a distinct yellow or greenish color and is often found incorporated into petrified wood.  Tyuyamunite occurs with carnotite (sometimes) but contains potassium rather than calcium.  I do have a sample of tyuyamunite in my collection.  It is supposed to be from Montana.  Amblygonite is found with cassiterite and topaz in pegmatites and can be pink and glassy in luster.  Triphylite is also precipitated in granite pegmatites but is black in color and softer.

The highway department has taken down my road signs for my shop.  They want me to buy new ones for nearly one thousand dollars, which is not feasible in the winter.  First I have to get the big saw fixed so I can generate more inventory.

cold weather

I had to email a customer and tell him that I just couldn't bully my way out to the shop and look for his rocks.  Yesterday I tried again and the walk was too slippery.  I have had an irrational fear of falling ever since a concrete step crumbled under me, which has been a few years ago.  Today it said -35 so I am delaying that cold trek again......

 Apatite is a very common phosphate used for fertilizer.  It is a source of fluoride.  Deposits are derived from fossil bone.  Monazite contains uranium and other important raw materials so is mined commercially.  It is used in isotope analysis to determine the age of rocks.  Vivianite and erythrite are secondary phosphates.  The latter is reddish and vivianite is colorless, blue or green.  Variscite is a beautiful material, sometimes used for carving or jewelry.  It is a hydrous aluminum-iron phsphate, white to greenish in color.

continuing mineralogy

I guess I had do some mop up on my study of mineralogy and blogging thereof.  The next consideration is phosphates, arsenates, and vanadates.  Many of these are useful as gemstones due to their attractive qualities.  The phosphate that comes to mind is turquoise.  It is found in igneous rocks and some pegmatities.  Its color and veining makes it very popular as a gemstone.

Lazulite is a blue magnesium iron-aluminum phosphate.  It could easily be confused with lazurite or lapis lazuli (a rock not a mineral).  Lazulite crystals are popular as gemstones due to their unusual blue color.

 

 

I was just reading an old geological survery online.  The subject was Hubbard County geology.  Hubbard county is where I live.  It is quite dull, and not referenced even once in my new Minnesota geology book.  To begin, there is no exposed bedrock.  The line of moraines running east to west may tell a little about the history of the movement of glaciers, to someone who can read the signs.  In the southeast corner there are a few pieces of soft, impure limestone, indicating there might be late cambrian era strata underneath the surface. 

I suppose one could dig deeper and look into the geochemical interaction between ground and lake water.  There are also soil surveys, aerial maps, and charts of bedrock geology.  There is also the study of sediment from lakes that were left behind by melted ice glacier.  

I started reading my new book in earnest.  It is Minnesota's Geology by Ojakangas and Matsch.  I like it better than my old MN geology book, which is really too old, because it has more humor and human interest. 

The first chapter is a briefing about geology in general with just a few specific Minnesota references.   It starts out with an exciting version of how the Minnesota River formed, when a melting glacial lake overflowered and flooded through a valley, eroding it and revealing much older rocks.  This may have occurred twelve thousand years ago.  Some geological dates are mind-boggling;  12 thousand years doesn't seem that long.  Or does it?  Another fact that stood out is that Minnesota doesn't have any gemstones of significance. But collectors can find agates and other quartz minerals that are quite interesting. 

 

Am I a Neanderthal?

On occasion I work for Mechanical Turk.  I do HITs.  HITs are human intelligence tasks that can't be done by artificial intelligence.  I get paid a little now and then.  Today I worked for AccessDNA.  The questionnaire I filled out reminded me that I am a European Caucasian, my relatives had an aneurysm, colon cancer, anemia and depression, and I take a lot of meds.  AccessDNA is a useful site for people planning pregnancies, finding out what they're going to die from, who their father is or if they are indeed a father, and stuff like that.  There are lots of links for people who need help because of their genetic inheritance.  I have also received a promise that I will be notified of DNA souvenirs, gifts, and so on when and if they become available.  A report was generated on me, and I received the summary, which was frustrating and leaves me wondering if there was more.  For some reason the file was corrupted and I had to open it in Appleworks.

 But there was a link on that site that fascinated me.  A scientist is sequencing Neanderthal DNA and so far he concludes that Neanderthal and modern man interbred.  So Neanderthals probably contributed to our gene pool.  That would explain a lot.

more sulfates

There are a few more sulfates covered in mineralogy texts.   Bronchantite is formed by oxidation of copper sulfides in arid areas. It is green. Antlerite is similar to bronchantite but the crystals are more often tabular or fibrous. It is also green.

Glauberite is described as a double salt. It is found in arid areas such as Chile, the dry lakes of California, Egypt, Russia, and India. Its crystals form in salt deposits. It is gray, yellow, or colorless.

Alum is a sulfate with commercial applications. Its most recognizable form is in the styptic pencil.

Got a notice from MN DOT. My rock shop signs have to be replaced, even though to me they look new, to the tune of nearly one thousand dollars.Maybe I will reinvent the rock business, and myself.

 

http://www.oliviahoff.com

barite group of sulfates

The barite group of sulfates includes barite, celestite, and anglesite. Barite is used in paints and papers. It is also added to drilling mud in oil wells to control the specific gravity of the mud. Celestite is found throughout the world, mostly in sedimentary rocks. It is named for its distinct pale blue color. The nicest blues seem to be from Madagascar. Anglesite is usually an alteration product of galena. It is usually mixed with cerussite, a carbonate. It is usually colorless, white or gray but can be yellow, blue or green.

I painted a dinosaur on sandstone today.  An albertosaurus. It was a tyrannosaurid, but smaller than rex. And I am not the worlds best artist.

 

http://www.oliviahoff.com

sulfates

Sulfates are oxygen and sulfur compounded with one or more metals. There are over 150 named varieties, due to the number of possible combinations.  Gypsum is the most common. The distinct varieties are alabaster, selenite, and satinspar. Gyppsum is used in plaster of Paris.

Anhydrite is less common than gypsum. It is associated with salt beds and has a pearly luster. It takes up water and converts to gypsum.

Epsomite is common as epsom salts. It is found in mineral waters and deposits, and contains cobalt, zinc, manganese and nickel.Now to the metaphysical Adularia is called the stone of the Goddess. It is a form of moonstone that can be faceted. It is clear with a beautiful iridescence, and is quite rare Many of the deposits in Sri Lanka have been depletes. Some has been found in the Austrian alps. It is valued as a means of inward journeying and symbolizes tranquility.

 

http://www.oliviahoff.com

 

http://www.oliviahoff.com