Spearhead (red Sandstone) With Gold Inside?

[SHB111]

8 minutes ago, GB_Amateur said:

Exactly how did you measure the specimen's volume?

Graduated cylinder

filled it with water to a depth taller than the spearhead. Took a reading. Dropped the spearhead in. Took another reading. Did subtraction.

then to double check myself I weighed the difference in volume on a scale. Since 1 gram of water displaces 1 cubic centimeter of volume I figured it was a good way to check to make sure I didn’t read wrong.

[GB_Amateur]

3 minutes ago, SHB111 said:

Graduated cylinder

filled it with water to a depth taller than the spearhead. Took a reading. Dropped the spearhead in. Took another reading. Did subtraction.

In my experience that method can have significant uncertainty (often called 'error' although not synonymous with 'mistake' in this use case).

I prefer the Archimedes Principle method.  I do that by suspending the sample below the scale via a bail.  The bail is in intimate contact with the scale's platform (and nothing else other than the attached sample).  Once stable I zero (tare) the scale.  Then I bring up from the bottom a container of water, large enough to completely envelop the sample in water, making sure that the sample is completely submerged but simuntaneously not touching any part of the container (in particular not letting it come to rest on the bottom!).  The scale will read a negative value whose magnitude is the buoyant force.  Since water has a density of 1.00 g/cm^3, if the scale is read out in grams (or its reading converted to grams) then the item's volume is the buoyant force (in gram units) divided by the density of water (1.00 g/cm^3), in cubic centimeters.

The biggest error (in this case I do mean 'mistake' 😁) I see people make is not accounting for the uncertainty in the volume measurement.  For example, with a scale of smallest readout digit being 1/10th of a gram, they will divide the item's dry weight (let's use 10.3 g as an example) by the volume (0.9 g / 1 g/cm^3 in this example) and conclude the specific gravity is  (or density is 11.4 g/cm^3).  In fact, the volume is just as likely 0.85 cm^3 and just as likely 0.95 cm^3 as it is 0.90 cm^3.  Thus the density should be stated by the bracketed extremes:  10.3/0.95 <= specific gravity <= 10.3/0.85, or (doing the division) the item has a specific gravity between 10.8 and 12.1.  And all that assumes the scales are properly calibrated and there were no air bubbles on the sample -- more sources of uncertainty.  I even ignored the numerator's uncertainty -- 10.25 g --> 10.35 g although that effect is small compared to the denominator's uncertainty in this case.  Doing that gives a range of 10.8 to 12.2 for the specific gravity.

One more source of systematic uncertainty is the volume of the sample's support.  For example, suppose the sample is a rock.  Rocks don't typically have a hook for the bail to grab!  The minimum amount of the tiniest wire is one option, but then the amount of that wire that is suspended in the water should be measured or calculated and corrected for in the final volume determination.  For small samples I use monofilament sewing thread which is so fine it's almost invisible (I think it has 0.0040 inch diameter = 0.10 mm) and its volume can be ignored in most cases.  But tying a knot in that can be quite the challenge!

 

[SHB111]

1 hour ago, SHB111 said:

Graduated cylinder

I can see this hobby taking up a lot of my time, lol.

But I’m game. Any certain equipment specifications I should be aware of - type/brand scale, etc or anything else I should get to mitigate error as much as humanly possible?

[GB_Amateur]

2 hours ago, SHB111 said:

Any certain equipment specifications I should be aware of - type/brand scale, etc or anything else I should get to mitigate error as much as humanly possible?

There was a thread here the last couple weeks about choice of scales.  My approach is to get an affordable set of scales and an affordable set of calibration weights.  The latter don't lie and will tell you when your scale is doing so.  😁  But if that's the case, I can make a calibration curve in the worst case that translates a reading to an actuaI reliable value.

I have four scales -- one a hanging scale (for multi-kilogram range) and three smaller, each one covering a least significant digit range (one, two, and three decimal place) for the gram scale.  As far as top end (max weight before overflow), I try to find one with the largest capacity which still fits my number of gram decimal place requirement.  My total investment for four scales and calibration weights is under $100.  I bought them over 5 years ago and all still work and are accurate.

[SHB111]

Sounds like a good plan, hate needing a tool/equip and having to wait on it, may as well buy a setup like that and be prepared. Appreciate the info. 
Since testing kits for gold/silver/platinum are inexpensive, and so are diamond testers, might as well grab that as well. Maybe a spectrometer too, few hundred bucks possibly well spent.

[SHB111]

15 hours ago, GB_Amateur said:

There was a thread here the last couple weeks about choice of scales.  My approach is to get an affordable set of scales and an affordable set of calibration weights.  The latter don't lie and will tell you when your scale is doing so.  😁  But if that's the case, I can make a calibration curve in the worst case that translates a reading to an actuaI reliable value.

I have four scales -- one a hanging scale (for multi-kilogram range) and three smaller, each one covering a least significant digit range (one, two, and three decimal place) for the gram scale.  As far as top end (max weight before overflow), I try to find one with the largest capacity which still fits my number of gram decimal place requirement.  My total investment for four scales and calibration weights is under $100.  I bought them over 5 years ago and all still work and are accurate.

Gotta figure out what this is in this thumb scraper now. See attached.

[Jeff McClendon]

That is a little cavity lined with quartz crystals. That can happen quite often in flint, chert, chalcedony and agate since they are cryptocrystalline forms of quartz. Any crack, crevice or cavity within those varieties of quartz can make enough room for secondary deposits of quartz along with other minerals including gold to form crystals.

[SHB111]

10 minutes ago, Jeff McClendon said:

That is a little cavity lined with quartz crystals. That can happen quite often in flint, chert, chalcedony and agate since they are cryptocrystalline forms of quartz. Any crack, crevice or cavity within those varieties of quartz can make enough room for secondary deposits of quartz along with other minerals including gold to form crystals.

Nice. All kinds of nice surprises. Multi-layered entertainment.

[Gold Seeker]

Even if your spear point is modern it could still be gold in it, have it tested with a spectrometer as you said you were going to, just an FYI spectrometers cost a lot more than a few hundred dollars.

[Steve Herschbach]

I don’t see anything that would make me think for two seconds there is gold in that spear point. Beyond normal microscopic background values that is. First rule of prospecting is learn what to look at, and what to simply ignore. The planet is full of stuff that looks like gold to people, but is not. I’m kind of amazed 5 pages has been spent on it. But hey, that’s what forums run on!