Jump to content
Kingofthekats

Is this opal it showed up as 2.3 on specific Gravity

Recommended Posts

Kingofthekats

I know this is not a fossil but I need help with identifying the rock

DSCN6873.JPG

DSCN6879.JPG

Share this post


Link to post
Share on other sites
Darktooth

I am going to say quartz

Share this post


Link to post
Share on other sites
Innocentx

Is that a spear point?

Share this post


Link to post
Share on other sites
Kingofthekats

Yes atlatl dart point I found it in the ground yesterday

Share this post


Link to post
Share on other sites
WhodamanHD

I'd guess arrowhead, based on the fact that most of your finds are from the surface and atlatls were not in wide use by the woodlands, which are more recent. As for the material, looks like quartz (opal is a type of quartz) which was probably used for it durability as well as its shark flakage (technical term:P [real term may be sharp cleavage? I don't know if quartz has a specific cleavage plane{s}])

Share this post


Link to post
Share on other sites
Kingofthekats

I found this two to three feet deep in the ground

Share this post


Link to post
Share on other sites
WhodamanHD
2 minutes ago, ynot said:

Sorry for this @WhodamanHD, but most of this is wrong.

Yes - probably an arrowhead, as most atlatl points are larger. It is made from quartz.

There are a lot of ways that older artifacts can be brought to the surface, so that is not an age indicator as a general rule.

During the period of time that atlatls were in use the forests looked much different than the present day, so they could be found where it is forested today.

Opal is NOT a type of quartz. It is silica but does not have the structure of quartz. It is classified as a mineraloid and not a true mineral. Opal is also much softer and more brittle than quartz.

Quartz does not have a cleavage. (some say it has a weak one but I have never seen any evidence to back that up.)

The way that both opal and quartz break is called a conchoidal fracture (same as glass) and is a trait that was sought out for "knapping" (the process of making a stone tool.)

There is no term of "sharp cleavage" - a crystal either has cleavage or it does not. Cleavage can be described as weak, poor to strong, good.

Thank you for the information, I'm not sure why but for some reason opal was a quartz in my mind (embarrassingly enough opal is my birthstone). When I said woodland Native Americans, this describes the most recent grouping of eastern Native American tribes, here's a Wikipedia article: https://en.m.wikipedia.org/wiki/Woodland_period. I assumed that the topsoil was youngest but you are right, admixture is probable. Conchoidal fracture was the term I was looking for (thank you for telling me it!)

Don't be sorry, I'm happy to learn! As Douglas Adams once wrote: “A learning experience is one of those things that says, 'You know that thing you just did? Don't do that.”

Share this post


Link to post
Share on other sites
Sagebrush Steve
On 7/30/2017 at 5:02 PM, Kingofthekats said:

I know this is not a fossil but I need help with identifying the rock

DSCN6873.JPG

DSCN6879.JPG

I'm going to agree with the others that from its visual appearance this looks like quartz.  But it's specific gravity of 2.3 is well outside the range for quartz, which is 2.65 plus or minus 0.01.  It's possible this specimen has internal voids that reduce its weight compared to its volume.  Also make sure that when you measure its weight in water that you put a small drop of liquid soap in the water to reduce its surface tension.  Otherwise air bubbles may stick to the rock to throw off the result.  A specific gravity of 2.3 is very close to that of obsidian (the classic material for arrowheads) at 2.4, but this looks nothing like obsidian.

Share this post


Link to post
Share on other sites
WhodamanHD

It's certainly a nice specimen, Whoever owned it must have been proud, maybe of high status. Or maybe they just couldn't find any chert or flint, and were forced to use quartz. It's not the easiest to knapp quartz, I've tried many times unsuccessfully. Wonder why they left it, the arrow must have been lost.

Share this post


Link to post
Share on other sites
ynot

@Kingofthekats,

Some opal can look the same as a milky quartz and there seems to be a question about the specific gravity of this point.

 

I suggest that You redo the specific gravity test, just to be sure. 

Also opal will have a "waxy feel" to it where quartz will feel like glass.

 I have seen very few tools made from opal. I think it was to fragile and would break to easily so was only used as a "last resort" when more suitable rock was not available.

 

 

@WhodamanHD,

Most of the pre columbian peoples of the americas used what was readily available in the area they lived in or would trade for better material from other areas. Since everything had to be carried by hand the further from the source the rarer the rock would be (hence the more valued it would be). So if quartz (or opal) were common in the area then the stone would not be prized over the workmanship.

There is no source for obsidian in the area around where I live, but there is around 20% of the points in the area that are made from obsidian.

Share this post


Link to post
Share on other sites
WhodamanHD
8 hours ago, ynot said:

 

 

 

@WhodamanHD,

Most of the pre columbian peoples of the americas used what was readily available in the area they lived in or would trade for better material from other areas. Since everything had to be carried by hand the further from the source the rarer the rock would be (hence the more valued it would be). So if quartz (or opal) were common in the area then the stone would not be prized over the workmanship.

There is no source for obsidian in the area around where I live, but there is around 20% of the points in the area that are made from obsidian.

Closest area with quartz to raubsville would be my area and a little to the northwest of here, would have been a few days hike. Certainly no opal in the area. So not an incredible distance, still required trade though. In his area most rocks a sedimentary which are unsuitable for arrowheads.

Share this post


Link to post
Share on other sites
Plax

have been corrected a number of times by archeologists when I used the term "arrow head". They call them bifacial tools and they can be used in a number of ways. Not just arrowheads or atlatl darts. Am good with whatever anyone wants to call them though of course!

Share this post


Link to post
Share on other sites
Kingofthekats

I am taking it to a gem place today maybe they can tell if it is opal possibly

Share this post


Link to post
Share on other sites
drobare

This looks almost exactly like some quartzite arrowheads I have seen that came from southern Maryland..

 

I'm still trying to find one of those myself.. nice..

Share this post


Link to post
Share on other sites
ynot
1 hour ago, Kingofthekats said:

I am taking it to a gem place today maybe they can tell if it is opal possibly

My money's on quartz.

Share this post


Link to post
Share on other sites
sTamprockcoin

I Have an identical piece from Montgomery/Bucks county PA and it is w/o a doubt quartz. From my research and discussions with archeologists it seems that there may have been both significant trade along the river systems and travel to specific sites for specific materials.Our ancestors thought nothing of walking for a week to get somewhere so a few days walk for quality material is not out of question.

Share this post


Link to post
Share on other sites
Kingofthekats

So I did the test again and added soap and now it shows up as 2, weighs 6 grams, filled the cup of water then a drop of soap then I tared it back to zero, then put the arrowhead in the cup with water and came to 3 grams which I divided 6 and 3 and comes to 2

Share this post


Link to post
Share on other sites
WhodamanHD
1 minute ago, Kingofthekats said:

So I did the test again and added soap and now it shows up as 2, weighs 6 grams, filled the cup of water then a drop of soap then I tared it back to zero, then put the arrowhead in the cup with water and came to 3 grams which I divided 6 and 3 and comes to 2

Quartz's specific gravity is 2.65 so accounting for error is about right. There's little question that this is quartz.

Share this post


Link to post
Share on other sites
Kingofthekats

So it is not quartz?

So quartz is 2.65 and this 2.0 I don't get it

Share this post


Link to post
Share on other sites
WhodamanHD
5 minutes ago, Kingofthekats said:

So it is not quartz?

So quartz is 2.65 and this 2.0 I don't get it

Flaws in the stone, other minerals, and human error (even small changes can create problems, I've never gotten an accurate reading with the test) it's probably close enough.

Share this post


Link to post
Share on other sites
Sagebrush Steve
3 hours ago, Kingofthekats said:

So it is not quartz?

So quartz is 2.65 and this 2.0 I don't get it

That's a pretty large discrepancy for a 6 gram specimen.  I've done hundreds of specific gravity measurements on gemstones smaller than that and never see that much of a discrepancy.  So the possibilities are:

1. Your scale is not sensitive enough for such small specimens.  What is the range and resolution of your scale?  Ideally you should use a scale with 0.01 gram resolution but you could probably do ok with one that has 0.1 gram resolution.

2. It's not quartz.  The specific gravity is in the range of obsidian but it doesn't look anything like obsidian.  It's also in the range of opal but I would highly doubt it's opal.

3. You are somehow making an error in the measurement.  In reading your description it sounds like you are doing things correctly, so I'm not sure what to say there.  Make sure the specimen is fully immersed in the water and not touching the sides or bottom of the water container.  And be sure your water container is not so heavy that your scale runs out of measurement range when you add the extra weight of the immersed specimen.

4. It is quartz with significant levels of fractures, or voids.  That could be possible but there is no way to tell for sure from photos.

Share this post


Link to post
Share on other sites
Sagebrush Steve

And in case you missed it, here's a post I made recently that describes how to measure specific gravity accurately.

 

 

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now


  • Recently Browsing   0 members

    No registered users viewing this page.

×