Written by the TreasureGuide for the exclusive use of TBR2020.blogspot.com.
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| Flag Over Berconshire Shipwreck Off Vero During Isaias. |
I'm not sure of the source, but this photo has been circulating. I think it was from a news agency. I've seen it on Twitter and various other sources.
The Berconshire, or Boiler Wreck, sunk in 1894 and is a popular diving spot.
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If you ever looked at sand under a microscope you might be surprised by the variety of grains and colors that you see. The encrusted sand sticking to a previously buried metal objects can be especially rich in color. You might see clear quartz, white opaque bits of coral, beige pieces of shell, but also blue, green yellow and even bright red. Like me, maybe you've wondered what caused those bright colors and where they came from.
For more about that see https://www.dgs.udel.edu/delaware-geology/piedmont-and-plate-tectonics
Be careful not to confuse black sand with decayed organic material, which can look something like black sand. Of course that decayed material will not bother your metal detector.
If you are a Treasure Coast detectorist, you have probably seen black sand. It does not appear on all Florida beaches and can disappear and reappear at different times.
You probably also know that black sand can cause problems for detectorists, but you can learn to deal with it. Some detectors are bothered by it more than others, but don't give up, you can learn to detect in black sand.
Some locations do not have black sand. In South Florida, for example, you won't find much black sand. That sand is made mostly of shell and coral bits.
Below is a table showing a few of the minerals commonly found in Florida beach sand.
Quartz, one very common element, is white and non-magnetic. Ilmenite, on the other hand is black, and is one of the heavy minerals that is sometimes in beach sand.
You can see from the chart above that ilmenite is magnetic and a good conductor of electricity. You can therefore understand how it might cause problems for a metal detector.
Another example of a heavy mineral that is sometimes found in Florida sand is rutile, which is non-magnetic but, as you can see from the above table, is a fairly good conductor of electricity.
Black sand often is found in beds, strips or sheets of varying thickness and at different depths. If you get a fresh cut on a beach with black sand, you can often see the edge of multiple layers of different thickness.
The Nineteenth Annual Report of the Florida Geological Survey presents an article entitled Statistics of Mineral Production in Florida During 1926. Here is the link.
The table above and the following excerpts are taken from that report.
Limonite is the mineralogical name for the hydrous iron oxide which
gives most of the yellow, orange, and red colors to sands. It usually occurs
as thin coatings, firmly adhering to the grains and extending into the cracks,
and is also present in the clay occurring mixed with many sands. Iron
oxide occasionally cements sand together forming hard lumps called concretions, or even continuous layers of sandstone...
Little variation is found in the specific gravity of sand grains, especially when we limit ourselves to a consideration of Florida sands. Quartz has a specific gravity of 2.65, calcite 2.7:2 and pebble phosphate about 2.5. However, there are much greater variations than this in the weight per cubic foot or cubic yard because the amount of pore space, or voids, between the grains is widely different in different sands, and in the same sand under different conditions. A sand, all of whose grains are about the same size, will have a larger percentage of voids amid smaller weight per cubic yard than one in which the spaces between the larger grains arc partly filled with smaller ones. The same sand will of course have a greater weight per unit volume when closely packed than when loose. Moisture content is another thing to be considered. A given volume of sand will usually weigh less when damp than when dry because each grain of the wet sand is separated from those nearest to it by a thin film of water. In other words, adding moisture to a sand will cause it to swell and become less dense. Thorough soaking, however, will cause the sand to pack and occupy practically the same volume as when dry. Statistics gathered by the United States Geological Survey show that a cubic yard of sand may weigh anywhere from 2000 to 4000 pounds while the average weight is 2,665 pounds for sand and 2,320 for gravel...
Practically all quartz sand contains a small proportion of grains of various minerals which are considerably heavier than quartz, feldspar and calcite and may be spoken of collectively as heavy minerals. Of these, ilmenite seems to be the most common in Florida but a number of others including tourmaline, zircon, and rutile are almost invariably present, while monazite, staurolite, epidote and garnet are rather common...
Here is a illustration from the Geological Survey Report showing a beach profile from an area called Mineral City, up by Jacksonville. Mineral city was of course named for the minerals found in the sand, which were once commercially mined.
You will often find black sand near the foot of the dunes and above the wave swept beach as shown in the above illustration from the geological survey report.
Now you know a little more about black sand and why it can cause problems for metal detectors. In a few older posts that you'll find in treasurebeachesreport.blogspot.com, I've described methods for metal detecting over black sand.
Metal detecting is a great hobby that connects to a wide variety of disciplines, including, as you see today, geology.
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Gold continues its upward trend and made it over $2000 per oz. yesterday.
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If you returned from the beach being disappointed that you didn't find anything old, consider this.
Old was everywhere. You were walking on it. It was between your toes. It was everywhere. Even in your DNA.
Everything in the universe goes back to the beginning of time.
The eye never has enough of seeing,
nor the ear its fill of hearing.
9What has been will be again,
what has been done will be done again;
there is nothing new under the sun.
10Is there anything of which one can say,
“Look! This is something new”?
It was here already, long ago;
it was here before our time. (Ecclesiastes 1:8-10.
Things look as big or small as a person's perspective allows. A slight change of perspective can open up a marvelous new view.
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There are no new storms to watch and the surf has returned normal summer size.
Happy hunting,
TreasureGuide@comcast.net