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New Agate Book for 2011

To be published around July 2011:  Agate in Thin Section (Studies on Agate series)

Over 20 different agates have been selected because their appearance suggests a thin section examination might reveal new information about the manner of crystallisation, structure, band relationships or possible genesis.
Each agate is discussed separately and the same format will be used to describe each individual agate. Initially, a brief description is given about the background of a particular agate, followed by relevant references with a description of the thin section including photo/ micrographs. Some observations will allow comment on the apparent genesis of the agate.
Introduction Describes the preparation of a rock thin section starting with a sample of macrocrystalline quartz. The changes in the polarisation colours are photographed in colour as the section is ground down from a thickness of 1.30 mm down to a standard thin section of 0.03 mm. Agate is microcrystalline quartz but both macro and microcrystalline quartz show the same polarisation colours. Helpful hints are given for the amateur to make their own thin sections. Particularly exciting is the ability to examine agate development that formed tens or even thousands of millions of years ago and, of course, each agate observation is unique to that particular sample.
The rest of the book will look at around 25 agates dealing with observations on thin sections.
Some of the agates selected for thin section preparation and examination (scale bar = 2 cm):


book2011_clip_image001 1. Rio do Sul, Brazil. Horizontally-banded agates are assumed to be gravity controlled. The sample shown here is typical and reveals an initial set of horizontal bands followed by an upper region of wall-lining agate. A thin section will show the relationship between the two types of banding.
   
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2. Fairburn, South Dakota, USA. This agate shows an interesting formation of limestone followed by clay with red agate. Rhythmically banded agate completes the sample.

   
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3. Cottonwood Springs, Texas, USA. A black and orange chalcedony has formed on a basalt host.  Does the chalcedony texture change as well as the colour?

   
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4. Burn Anne, Galston, Scotland. A large slab of agate shows some peculiar tubular growths in a block of vein agate. The relationship between the tube-like growths and the red and yellow colouration will be shown in thin section.

   
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5. Mount Somers, New Zealand. A peculiar piggyback-type agate is common in this area. The relationship between upper and lower agate growth will be examined.

   
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6. Dulcote, Somerset, England. The only commercial source of UK agate in the last century, but are these really agates or just banded macrocrystalline quartz?

   
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7. Lyme Regis, Dorset, England.  Agates from here show a sharp transition from a granular quartz and limestone background to an attractive agate centre.

   
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8. Nebraska Blue, Nebraska, USA. These interesting navy-blue agates are often found intermingled with the siltstone host.

   
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9. Bobonbong, Botswana. How does the banding change in agate? Selected sections are cut parallel and at right angles to each other. The banding development can be tracked using thin sections.  

   
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10. Las Choyas, Mexico. Agates from this area vary in size and colour and, together with the host, produce a combination that is uniquely spherical.

   
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11. Union Rd, St Louis, USA. The formation of white limestone   agate and a centre of calcite crystals is particularly interesting.

   
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12. Sierra Santa Lucia, Mexico. Agates from this region produce a complex pattern known asCrazy Lace agate.  The relationships between the bands are examined.

   

At least 10 other examples of agate will be added to the list.

If you wish to be informed when the book is in print, then please let me know via the Contact e-mail address. I will acknowledge receipt but there is no commitment on your part. The complete set of agates  will eventually be given on the web site and you can then make up your mind whether the book is for you.  An e-mail will inform you when the book is in print and anticipated costs will be ~ £20.