tachylyte (or tachylite)

[Gary Vines]

This is called Tachylyte in a report (not one of  mine) – but  it is  what I call Hornfels. The examples in geology illustrations show a more diverse and grainy stone despite it being defined as a form of basaltic volcanic glass..

 

 

The really distinctive thing about it (whatever it is called) is the patina, which is pale grey when first found, but quickly darkens from handling – I presume body oils fill the surface – you can see this happening in the example along the ridge lines. You can see on this piece the recent break showing almost black.

 

The thing about it, is I have only ever found a few bits at a time on sites around Melbourne and central Victoria. Where does it come from? Is it abundant anywhere?

 

All the examples I have seen in archaeological assemblages have this distinctive patina and dark interior and similar grain fineness. I suspect it is a material that might be sources to very specific locations – like Greenstone).

 

 

Gary Vines

 

 

 

[Amy's Gmail]

Hi all,
I'm looking to buy some good quality scales - if you have any sitting around that you'd like to sell please contact me,
Cheers,
Amy
amywa...@gmail.com

[Gary Vines]

You have just hijacked a thread

This email is to bring it back on track.

If you have a new topic, please do not reply to an existing ozarch
message and change the subject heading - but instead send a fresh
email to oza...@googlegroups.com, of hit the +new post, on the web
site

thanks

gary Vines

> amyway1...@gmail.com

[Tessa Corkill]

Hi Gary

Tachylyte certainly exists in Victoria - see for e.g. http://www.minsocam.org/ammin/AM23/AM23_277.pdf and your photo seems to fit descriptions and pictures I have see.

But why would you call it hornfels (metamorphic not igneous)?  I know that there are a number of varieties of hornfels but the ones I know best (in the Sydney area) are suitable for grinding, not flaking. When identifying hatchet material, people (archaeologists) often used to misidentify hornfels as basalt or what they called 'fine grained basic', mostly on the basis of colour I think. Has the rock in your photo been analysed by anything like XRD or XRF?

Tessa Corkill

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[Richard Wright]

Gary

I don't have my article to hand, but I rather think that tachylyte occurred among the artefacts at Green Gully.

1970  "Flaked stone material from GGW-1" in "The Green Gully Burial", Memoirs of the National Museum of Victoria, 30:79-92.

Given that the GGW-1 site predates the severing of Bass Strait, I remember discussing with Rhys Jones the possibility of tachylyte being transported to Tasmania, and Darwin glass being transported from Tasmania to Victoria.

Alas, I don't know that such transportation has ever been shown to exist.

Richard

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[Gary Vines]

I may be completely off calling it Hornfels, but all the examples of
Tachylyte I have been able to find are completely different from this.
Surely others have found the same patinated material and have a more
discrete name for it.

Gary

[john...@ozemail.com.au]

 

Hi Gary,

Tachylite is not hornfels.

I do have a bit in my backyard though.

Cheers,

 

John

(Sydney)

~~~~~~~~~~

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Tue, 14 Aug 2012 23:24:01 -0700 (PDT)

Subject:

Re: {OzArch} tachylyte (or tachylite)

[john...@ozemail.com.au]

 
Hello Gary,

Hornfels often (but not always) has minute equant pits showing on the surface (where tiny porphyrocrsts have weathered out) - it is contact metamorhic in origin.

Those pits are easily seen with a hand lens, or even with the naked eye.

Tachylite often (but not always) has minute lighter coloured lines in it, all sub-parallel (because it has flowed - very chilled basaltic melt).

Quite commonly (at least in NSW) that's sufficient to distinguish the two.

But really desperate cases might require a thin section?

Cheers,

 

John

 

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Sent:

Wed, 15 Aug 2012 03:33:31 +0000

Subject:

{OzArch} tachylyte (or tachylite)

This is called Tachylyte in a report (not one of  mine) – but  it is  what I call Hornfels. The examples in geology illustrations show a more diverse and grainy stone despite it being defined as a form of basaltic volcanic glass..

 

 

The really distinctive thing about it (whatever it is called) is the patina, which is pale grey when first found, but quickly darkens from handling – I presume body oils fill the surface – you can see this happening in the example along the ridge lines. You can see on this piece the recent break showing almost black.

 

The thing about it, is I have only ever found a few bits at a time on sites around Melbourne and central Victoria. Where does it come from? Is it abundant anywhere?

 

All the examples I have seen in archaeological assemblages have this distinctive patina and dark interior and similar grain fineness. I suspect it is a material that might be sources to very specific locations – like Greenstone).

 

 

Gary Vines

 

 

 

--

[Colin Pardoe]

Not my expertise at all, but in central western NSW along the n-s trending ridgelines of the western-most extent of the Great Dividing Range, one comes across similar materials. At its most lustrous, it has a passing similarity to chert [noted by Scott Cane, who noted that it wasn’t chert, but was a wonderful material for flaking control, and that a lot of the smaller backed blade production used this material]. It is very common in some parts and it also weathers to a light gray colour, similar to the picture. I had no idea about chronology of weathering, since most of the material had been exposed on the surface for a hundred years or more since the sheep conveniently got rid of the topsoil.

Some of the material has lines in it, which did not appear to be sedimentary and from John’s email, I now understand:

minute lighter coloured lines in it, all sub-parallel (because it has flowed - very chilled basaltic melt).

I had the enjoyable experience of corralling a mob [clast?, concretion?, conglomerate?] of geologists and asking them what this material might be – preferably in short words in English. After much discussion and terminology increasing in length, the final view was that it had started life as a volcanic, but been heavily silicified. So I use silicified volcanic or silvol in my terminology. Now perhaps I should use tachylite instead?

All the best,

Colin

 

Colin Pardoe Bio-Anthropology & Archaeology

16 Hackett Gardens, Turner, ACT 2612

phone  02 6248 7337

mobile  0428 69 2798

 

www.australianarchaeologicalassociation.com.au

www.aacai.com.au

 

From: oza...@googlegroups.com [mailto:oza...@googlegroups.com] On Behalf Of Tessa Corkill
Sent: Wednesday, 15 August 2012 3:55 PM
To: oza...@googlegroups.com
Subject: Re: {OzArch} tachylyte (or tachylite)

 

Hi Gary

[john...@ozemail.com.au]

 
Hi Colin,

Tachylite is not silicified volcanics either.

Have a look in the road cuttings just east of Lucknow ... good examples there from memory.

Sounds like your stuff may well be tachylite.

Cheers,

 

John

 

~~~~~~~~~~

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Thu, 16 Aug 2012 12:35:33 +1000

Subject:

RE: {OzArch} tachylyte (or tachylite)

Not my expertise at all, but in central western NSW along the n-s trending ridgelines of the western-most extent of the Great Dividing Range, one comes across similar materials. At its most lustrous, it has a passing similarity to chert [noted by Scott Cane, who noted that it wasn’t chert, but was a wonderful material for flaking control, and that a lot of the smaller backed blade production used this material]. It is very common in some parts and it also weathers to a light gray colour, similar to the picture. I had no idea about chronology of weathering, since most of the material had been exposed on the surface for a hundred years or more since the sheep conveniently got rid of the topsoil.

Some of the material has lines in it, which did not appear to be sedimentary and from John’s email, I now understand:

minute lighter coloured lines in it, all sub-parallel (because it has flowed - very chilled basaltic melt).

I had the enjoyable experience of corralling a mob [clast?, concretion?, conglomerate?] of geologists and asking them what this material might be – preferably in short words in English. After much discussion and terminology increasing in length, the final view was that it had started life as a volcanic, but been heavily silicified. So I use silicified volcanic or silvol in my terminology. Now perhaps I should use tachylite instead?

All the best,

Colin

 

Colin Pardoe Bio-Anthropology & Archaeology

16 Hackett Gardens, Turner, ACT 2612

phone  02 6248 7337

mobile  0428 69 2798

 

www.australianarchaeologicalassociation.com.au

www.aacai.com.au

 

From: oza...@googlegroups.com [mailto:oza...@googlegroups.com] On Behalf Of Tessa Corkill
Sent: Wednesday, 15 August 2012 3:55 PM
To: oza...@googlegroups.com
Subject: Re: {OzArch} tachylyte (or tachylite)

 

Hi Gary

Tachylyte certainly exists in Victoria - see for e.g. http://www.minsocam.org/ammin/AM23/AM23_277.pdf and your photo seems to fit descriptions and pictures I have see.

But why would you call it hornfels (metamorphic not igneous)?  I know that there are a number of varieties of hornfels but the ones I know best (in the Sydney area) are suitable for grinding, not flaking. When identifying hatchet material, people (archaeologists) often used to misidentify hornfels as basalt or what they called 'fine grained basic', mostly on the basis of colour I think. Has the rock in your photo been analysed by anything like XRD or XRF?

Tessa Corkill

On 15 August 2012 13:33, Gary Vines <GVi...@biosisresearch.com.au> wrote:

This is called Tachylyte in a report (not one of  mine) – but  it is  what I call Hornfels. The examples in geology illustrations show a more diverse and grainy stone despite it being defined as a form of basaltic volcanic glass..

 

 

The really distinctive thing about it (whatever it is called) is the patina, which is pale grey when first found, but quickly darkens from handling – I presume body oils fill the surface – you can see this happening in the example along the ridge lines. You can see on this piece the recent break showing almost black.

 

The thing about it, is I have only ever found a few bits at a time on sites around Melbourne and central Victoria. Where does it come from? Is it abundant anywhere?

 

All the examples I have seen in archaeological assemblages have this distinctive patina and dark interior and similar grain fineness. I suspect it is a material that might be sources to very specific locations – like Greenstone).

 

 

Gary Vines

 

 

 

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[Colin Pardoe]

I will the next time in the area – either to buy wine at Turner’s vineyard just up the road, or at the shoe place in Lucknow, where they have a good range of waterproof boots [yes, I was totally unprepared for the end of the drought…].

So, is it possible that there might be two kinds of rock under consideration, tachylite characterised by faint lines, and another heavily modified material? Am I back to square one? Could we please have someone put together little boxes with samples of likely materials by region?

All the best,

Colin

 

Colin Pardoe Bio-Anthropology & Archaeology

16 Hackett Gardens, Turner, ACT 2612

phone  02 6248 7337

mobile  0428 69 2798

 

www.australianarchaeologicalassociation.com.au

www.aacai.com.au

 

[Gary Vines]

Colin's idea of a sample stone type collection, is one several people
have talked about many times in the past. There used to be something
like this at AAV (at lest when it was still VAS). Perhaps an on - line
version with goold photos, distinguishing attributes and even an
identification key would be the go.

This example seems to show the difficulty of making comparison where
there are differences (and in my case at least, inadequacies) in
naming stone types. I don't think I was even able to find it in
Holdaway and Stern's excellent book and cd.

I get back to the specific illustrated archaeological example. It is
its very distinctive appearance as an archaeological artefact that got
me wondering. Examples from at least a dozen sites I have seen have
all been identicle - almost black interior (lice mattt black
porcelain), gray patinated surfaces - never any cortex, only a few
pieces in each asemblage, and nothing else in the assemblage like it.
It doesn't seem to have the difficulties of distinguishing within a
continum, like the problem between the course silcretes and fine
quartzites seemingly overlapping to the untrained (mine again) eye.
The problem here is that there does not seem to be an agreed single
name for it.

Gary Vines

[Tessa Corkill]

I find that rock classification is much like artefact classification, or even that of homo sapiens: what can be described as the same 'species' varies widely. Take the Bondi Point for example: there is a written classification which seems quite clear, but when you see a lot of them together they are likely to be very different in size, shape, material, amount of backing etc etc. Likewise people: size, shape, colour, the list goes on ...

But back to rocks: pictures of what can be included in a particular 'type' can look vastly different. A sample collection of stone types sounds a good idea but it needs an extensive assortment of each type or it's easy for a novice to think that all (for example) silcrete, IMTC, quartzite (and of course tachylyte) should look like the one in the collection. Anyway, what do geologists say about your rock, Gary?

Tessa C

Gary Vines

[Gary Vines]

I found the references in Holdaway and Stern, Record in Stone  2004. - illistrated in  Fig 1.22.2 on the CD not in the book - seems plausable - grey patina, dark interior, "formed by high temperature metamorphism of shale, was used quite commonly as a raw material in southeastern Australia. The flaking qualities of hornsfels are not dissimilar to those of fine-grained basalts" (p.24) They don't mention tachylyte at all.

 

Gary Vines

 

 

 

[Tessa Corkill]

OK, I take your point and humbly apologise - there obviously are such hornfelses. But it seems your rock might be the kind of hornfels that results from the metamorphism of igneous rock such as basalt, rather than the ones I am more familiar with that originated as sedimentary rocks and are definitely not good for flaking (see http://www.earth.ox.ac.uk/~oesis/micro/  for examples).

It looks as if the quote you give "the flaking qualities of hornsfels [?hornfelses] are not dissimilar to those of fine-grained basalts" might need amendment - it could be true of some, but not all.

Again I ask, what do the geologists say about the pieces you find?  If you don't have contact with any perhaps you could send me one or two small bits to show a couple that I know.

Cheers

Tessa

 

 

 

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[john...@ozemail.com.au]

 
Hello Colin,

 

The "talk Tachylite" page at Wikipedia has not been all that active of late:  http://en.wikipedia.org/wiki/Talk:Tachylite#.23

Here is a pic that Gary will like = http://farm7.static.flickr.com/6028/5878921269_800d463d60.jpg

Discussed at http://helenaheliotrope.blogspot.com.au/2011/06/hazard-of-living-in-new-places-is-that.html where you can also see that lava pats look rather like cow pats.

Hence looks can sometimes be deceiving but we all know that already.

The writer there writes "We found a few chunks of tachylite, a type of volcanic glass that forms when lava cools very quickly, without having time to crystalize at all. This is like obsidian, but basaltic instead of rhyolitic. They’ve found a couple arrowheads made of tachylite here, but most of the arrowheads found here are obsidian from nearby Big Southern Butte, or from an obsidian bed in Utah".

Where tachylite is of Tertiary flow basalt association as in NSW it may be full of malformed/compressed ?vesicles as i mentioned before ... I cannot find a photo of such exactly -- but this one is similar = http://fr.wikipedia.org/wiki/Fichier:Tachylite.jpg

Cheers,

 

John

 

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[Gary Vines]

Thanks for all the discussion and suggestions, unfortunately I am
just getting more confused here -

Clarke 2004 refers to Trachyte - an igneous volcanic rock with an
aphanitic to porphyritic texture.

Howes and Clarke 2010 refers to Tachylyte - a vitreous form of
basaltic volcanic glass.

My original illustration was purported to be Tachylyte but does not
match image samples of either of the above. For that matter it doesn't
really look like the Hornfels examples in geological texts I have
examined.

My rock is black inside, and dense, but could not be considered
glassy.

The closest I can find in visal appearance (colour, texture, contrast
between the black interior and grey patinated surface) is Langdale
Tuff -

http://www.dockmuseum.org/info.php?page=8&v=1&s=ARCHAEOLOGY&type=browse&t=objects&f=CATEGORY1&d=
which is also volcanic.

So possibly this is a specific form of one of the Spring Hill Volcano
rocks.

I will get a geol to have a look, and perhaps bring some samples along
to one of the stone tool workshops that will be coming up soon.

gary Vines

[Gary Vines]

One last comment

The AAv site and artefact records have material categories for
hornfels and trachyte, but not tachylyte

GV

[Sam]

Do you have any non-artefactual material you could get made into a thin section? Shouldn't cost more than $35 usually. Some petrographic services will give you a brief report identifying your sample but I'd be happy to have a quick look at it otherwise.

Sam Player.

[john...@ozemail.com.au]

 

Hello Sam,

Have you an address of anyone doing thin sections for $35 please?

I am interested too at that price.

I also have a petrographic microscope (somewhere?) --- it's been put away and never used now for many many years.

However that is the only really reliable way to tell the nature or rocks or stones --- outward appearances may often suffice but also can be very varied (or even deceptive occassionally).

Cheers,

 

John

 

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{OzArch} Re: tachylyte (or tachylite)

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[john...@ozemail.com.au]

 
Hi Gary,

The answer to your very understandable dilemma is posibly that "glass" devitrifies over time and the Tertiary (if that be what it be) was long time ago.

And/or glass is used for meaning non-crystallised ... perhaps 'chilled melt' could be a better idea because glass does not always look like the glass you might have a glass of water from.

For example, pumice is also chilled or glassy I imagine yet may not look like everybody's (or even anybody's) popular idea of glass?

Cheers,

 

John

 

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{OzArch} Re: tachylyte (or tachylite)

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