A question for Windustsearch

[vmtz]

Found this on one of my wanders. Looks worked to me. But I don't think it was finished. What do you think?

http://www.nmia.com/~daykin/axe.JPG

http://www.nmia.com/~daykin/axe_2.JPG

Vince

[Windustsearch]

Vince it looks like either basalt or dacite, but black dacite is rare. You would need a microscope to tell for sure, or know the geology of where it was found. Looks like either a hafted axe or a digging tool. The large size and lack of refinement says digging tool to me. Either way it would likely have been made within the last 3 thousand years.

Faltitude may be able to add. I really don't have an adequate backround for most areas outside of the NW.

Does it have more use wear on one of the ends? Lots of very small flakes removed and or a dulled edge when compared to other edges?

[Windustsearch]

Where did you find it?

[hydrotx]

Vince,
Like Winddustsearch asked, where is it from? It looks like a shale or slate from a distance to me. Most of the dacites I've seen have larger crystals showing and the basalts typically have more olivine (green) depending on the geologic environment.

[vmtz]

The larger edge is more blunt then the smaller. It was found in New Mexico about twenty miles North of Albuquerque.

[Windustsearch]

I'll take a look in our library on Monday to see if I can't find a match from that area. There is sure to be a local tool classification system that people are using in reports.

[vmtz]

It is not a shale or slate. My guess is that it is basalt. I don't know what a dacites is.

Vince

[hydrotx]

Vince,
According to my beat up college text, dacite is defined as follows - the dense volcanic equivalent of granodiorite. It contains plagioclase feldspar and quartz, both of which may occur as phenocrysts. The dark mineral is usually hornblende, but biotite is found in some varieties. Some glass may be present in the groundmass, but glassy equivalents of dacites are rare. Manual of Minerology, Klein & Hurlbut, 1985

Hope that clears things up :)

Regards,
Joel

[Bwana John]

I don't know what a dacites is
Dacite is a igneous extrusive rock that is low in Fe and Mg, and high in SiO(2). It is very similar to rhyolite. The low % of mafic minerals usually produces a light colored rock.

I believe the artifact is made of basalt. Look for the very small green x-tals of olivine, it may require a hand-lens.

[Bwana John]

You beat me to it Hydrotx,
Some glass may be present in the groundmass,
Thin section, and cross polers!

[Windustsearch]

No cutting thin sections from artifacts! Fargin geologists.

Dacite is easy to identify with a microsope. So is basalt and basalt metasediment. We have black dacite (San Juan Dacite) up here in the NW coast area, but it is rare in other places, usually more grey. Our (NW) basalt is jet black. There are areas where you can find it with the green olivine, but its not as common.

[Bwana John]

No cutting thin sections from artifacts!
Yea, like you never got a date from obsidian hydration.:devil:

[Windustsearch]

No! But it was common up until about 15 years ago.

I have to admit that I would, depending on the significance of the artifact.

[hydrotx]

Damn, I remember in college going to the min lab, getting lit and watching the igneous rock colors swirl under polarized light. Damn we geologists are an exciting group.

[vmtz]

Originally posted by hydrotx
Damn, I remember in college going to the min lab, getting lit and watching the igneous rock colors swirl under polarized light. Damn we geologists are an exciting group.

Some days you guys scare me. I still don't know exactly what you all are talking about, but I suspect I am about to learn something. Stand back.

Vince

[hydrotx]

here you go Vince, dacite thin section under polarized light....ewww....pretty

http://www.geocities.com/hydrotx/dacitelarge.jpg

And then some plag

http://www.geocities.com/hydrotx/plagioclase1-X.jpg

When you rotate the base of the microscope the appearance of the object changes colors, sort of like a kaleidoscope.