Karen,
I had a student leave a set of phytolith samples in the muffle
furnace here for several days by mistake. The temp was set at 500
degrees C. The silica phytoliths melted together. I have been
hesitant to say that phytoliths vitrify at around 800 degrees C after
this experience.
Linda Scott Cummings
>It would be very helpful if everyone could be more specific about what they
>mean by 'high temperature burning'. The temperature thresholds for
>wood/charcoal combustion and silica vitrification are quite far apart: wood
>chars at temperatures of 200-300 degrees C, all organic carbon will be
>burnt off by 500 degrees C, and silica phytoliths vitrify at around 800
>degrees C. Even the presence of fluxing agents such as K and CaO, which are
>abundant in wood ash, could only lower the melting temperature of silica by
>around 200 degrees C. It is therefore not possible for charcoal and
>vitrified phytoliths to co-exist in the same specimen.
>
>I think the glassy appearance of some charcoal is likely to be due to the
>presence of sap or resin, which would lose water and 'bake' during the
>charring process.
>
>Karen Milek
>Department of Archaeology
>University of Cambridge
>Downing Street
>Cambridge, CB2 3DZ
>United Kingdom
>
>
>--On 27 August 2004 12:38 +0100 Marco Madella <[log in to unmask]> wrote:
>
>>I agree with Linda in trying to avoid generalisation about phytoliths
>>in wood. The Carnelli et al article has indeed shown that many woody
>>plants from a temperate climate produce phytoliths but they were mainly
>>extracted from their leaves. Opal phytoliths in wood seem to be more
>>frequent in tropical plants (e.g. Acacia).
>>
>>I do also agree that vitrification is not related to presence of opal
>>phytoliths in wood.
>>
>>M
>>
>>Dr Marco Madella
>>Affiliated Lecturer, Department of Archaeology, University of Cambridge
>>
>>Research Fellow
>>Director of Studies in Archaeology & Anthropology McDonald Institute for
>>Archaeological Research St Edmund's College Downing Street,
>>Cambridge CB2 3ER (UK)
>>
>>Direct line: +44-(0)1223-763513 -- Lab phone: +44-(0)1223-333537 --
>>e-mail: [log in to unmask]
>>
>>On 27 Aug 2004, at 10:48, Susan Allen wrote:
>>
>>>Hello -- I attach a nice discussion of calcium versus silica
>>>phytoliths by
>>>Linda Scott Cummings regarding N. American and African woods. It was
>>>meant
>>>for the list, so please read on...
>>>
>>>Cheers,
>>>Susan Allen
>>>
>>>---------- Forwarded message ----------
>>>Date: Thu, 26 Aug 2004 12:20:48 -0600
>>>From: Linda Scott Cummings <[log in to unmask]>
>>>To: Susan Allen <[log in to unmask]>
>>>Subject: Re: deformed charcoal
>>>
>>>Susan,
>>>
>>>Phytoliths in wood can be either calcium oxalate or silica. For
>>>instance, Salicaceae and Fabaceae are calcium oxalates. Definitely,
>>>a one-wood-fits-all answers is not appropriate. Given the volumes of
>>>wood that we have examined, silica phytoliths are not an abundant
>>>inclusion in many North American types. In other words, silica
>>>phytoliths usually are not seen in thin sections and when we extract
>>>silica phytoliths from wood we burn a rather large quantity of wood
>>>from each species to recover silica phytoliths. This is in contrast
>>>with grass where you can see the phytoliths in the individual cells.
>>>There are some trees, however, that produce many silica phytoliths.
>>>Some that I've looked at from Africa are very silica rich. But
>>>vitrification does not appear to be related to phytolith content. It
>>>is too pervasive and occurs in too many taxa to be the result of
>>>melting silica phytoliths.
>>>
>>>Best Regards,
>>>Linda Scott Cummings
>>>
>>>>Hello -- I too have found wood that looks vitrified in samples from
>>>>Balkan
>>>>/ Eastern Mediterranean contexts. It is often olive, as Julie noted,
>>>>but I
>>>>have also seen this in oak charcoal.
>>>>
>>>>I had thought this was due to fluxing of
>>>>silicates already present in the wood under conditions of high heat,
>>>>but
>>>>Linda's comment and others raise the question of secondary burning as
>>>>possibly being more important.
>>>>
>>>>Regarding phytoliths in wood, I have read that while taxa such as
>>>>Salicaceae and Rosaceae are low in phytoliths, other taxa (some
>>>>Fagaceae,
>>>>Pinaceae, Ericaceae) do have abundant phytoliths. It seems that there
>>>>have been few studies of dicotyledonous wood phytoliths, so maybe the
>>>>verdict is still out or there isn't a one-wood-fits-all answer?
>>>>
>>>>Carnelli et al. 2004 have a nice article about alpine forest
>>>>phytoliths in
>>>>Review of Paleobotany and Palynology 129:39-65 that has excellent
>>>>SEM's of
>>>>several woody taxa.
>>>>
>>>>Best regards,
>>>>Susan
>>>>
>>>>
>>>>Susan E. Allen
>>>>Department of Archaeology
>>>>675 Commonwealth Ave.
>>>>Boston University
>>>>Boston, MA 02215
>>>>
>>>>tel. (617)353-3415
>>>>fax. (617)353-6800
>>>>
>>>>On Thu, 26 Aug 2004, Linda Scott Cummings wrote:
>>>>
>>>>> We also see this phenomenon in charcoal samples. We have done some
>>>>> experimentation and note the same result (glassy look) when we burn
>>>>> green wood at a high temperature. We get this result the first time
>>>>> we burn the wood, so reburning appears not to be necessary. Perhaps
>>>>> it is due to the presence of sap when the wood burns. There are not
>>>>> enough phytoliths in most wood to result in this look.
>>>>>
>>>>> Linda Scott Cummings
>>>>>
>>>>>>Hello, I have seen that glassy look in charcoal from the
>>>>>>"destruction level" at Gordion...the wood is pine, from beams burned
>>>>>>in a very hot fire (i.e., hot enough to deform the pottery, too, and
>>>>>>some of the wheat and lentils also have a gray look). I wonder ...
>>>>>>are there phytoliths in wood (i.e., silica) that might vitrify at
>>>>>>high temperature?
>>>>>>
>>>>>>Naomi.
>>>>>>
>>>>>>On Thursday, August 26, 2004, at 09:54 AM, Owen Davis wrote:
>>>>>>
>>>>>>>I find these in westernUSAarcheological samples, too. Here,
>>>>>>>charcoal for specialists probably isn't the answer. But, perhaps
>>>>>>>they might indicate burning of charcoal from an earlier fire -
>>>>>>>repeated use of a hearth. I have also thought the glassy appearance
>>>>>>>might result from high-temperature combustion.
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>Yes, experimentation is the best idea.
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>Owen.
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>-----Original Message-----
>>>>>>>From: The archaeobotany mailing list
>>>>>>>[mailto:[log in to unmask]] On Behalf OfVan Der Veen, Dr
>>>>>>>M.
>>>>>>>Sent: Thursday, August 26, 2004 4:42 AM
>>>>>>>To: [log in to unmask]
>>>>>>>Subject: Re: deformed charcoal
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>I have found this in my Egyptian material (Mons Porphyrites and
>>>>>>>Mons Claudianus), in press.
>>>>>>>
>>>>>>>This is likely to happen when charcoal, rather than wood is used
>>>>>>>for fuel, ie material is fired twice (usually specialist use of
>>>>>>>fuel, in my case in smithies associated with stone quarries)
>>>>>>>Though experimentation would be good idea to test this idea.
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>Marijke van der Veen
>>>>>>>
>>>>>>>-----Original Message-----
>>>>>>>From: The archaeobotany mailing list
>>>>>>>[mailto:[log in to unmask]]On Behalf OfBIAX Consult
>>>>>>>Sent: 26 August 2004 10:48
>>>>>>>To: [log in to unmask]
>>>>>>>Subject: deformed charcoal
>>>>>>>
>>>>>>>Dear botanists,
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>I am an archaeologist and am involved in wood and charcoal research
>>>>>>>in the Netherlands. Regularly I come upon the phenomenon in
>>>>>>>charcoal, that the cell walls of the wood seem to have melted and
>>>>>>>the cell structure has disappeared . These charcoal fragments have
>>>>>>>a metallic shine, are very hard and difficult to break. It often
>>>>>>>seems to occur in bark fragments first. Does any of you recognize
>>>>>>>this and does anyone have an idea what causes this or where I can
>>>>>>>find references to this phenomenon.
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>Thanks a lot and greetings from Pauline van Rijn
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>BIAX Consult
>>>>>>>Onderzoeksbureau voor Biologische Archeologie en
>>>>>>>Landschapsreconstructie
>>>>>>>Hogendijk 134
>>>>>>>1506 AL Zaandam
>>>>>>>tel. 075 616 10 10
>>>>>>>fax: 075 614 99 80
>>>>>>>E-mail [log in to unmask]
>>>>>>>
>>>>>>-------------------------------------
>>>>>>Naomi F. Miller
>>>>>>University of Pennsylvania Museum
>>>>>>MASCA-Museum Applied Science Center for Archaeology
>>>>>>33rd and Spruce Streets
>>>>>>Philadelphia, PA 19104
>>>>>>--------------------------------------
>>>>>>tel: (215) 898 4075; FAX: (215) 898-0657
>>>>>>www: [log in to unmask]" target="_blank">http:[log in to unmask]
>>>>>
>>>>>
>>>>> --
>>>>> Linda Scott Cummings, Ph.D.
>>>>> Paleo Research Institute
>>>>> 2675 Youngfield St.
>>>>> Golden, CO 80401
>>>>> USA
>>>>> (303) 277-9848
>>>>> fax: (303) 462-2700
>>>>> http://www.paleoresearch.com
>>>
>>>
>>>--
>>>Linda Scott Cummings, Ph.D.
>>>Paleo Research Institute
>>>2675 Youngfield St.
>>>Golden, CO 80401
>>>USA
>>>(303) 277-9848
>>>fax: (303) 462-2700
>>>http://www.paleoresearch.com
--
Linda Scott Cummings, Ph.D.
Paleo Research Institute
2675 Youngfield St.
Golden, CO 80401
USA
(303) 277-9848
fax: (303) 462-2700
http://www.paleoresearch.com
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