Null Rocks

[digdan]

I went out in the middle of no where and did some metal detecting. Miles and Miles from any civilization. I was surprised when my detector came up with a Null response, yet I was not discriminating. Almost like I needed to put more negative on my ground balance. Then I noticed that this only happened in very tight pockets. I soon found that there was a type of rock causing this issue. Here is a link to a high res of these rocks :

High Res Black Negative(NULL) Rocks

I am a noob so I'm sure this is something that has been mentioned a million times over, but it would be nice if someone could tell me what these things are and why they are making my metal detector freak out.

Thanks in Advance!

[prizm-pal]

Dan I cant help you...maybe why no one has responded...but hope you figure it out good luck! Chick!

[PAPPY]

Could very well be meteorites

[schoser]

some rocks will do this because they have high iron content...iv'e come across a rock like the gray ones you see there, made my detector see it as metal too... maybe pappy is right ...they could be meteorites...especially the biggest one there thats more red/brown colored.

[ERnurse]

does a magnet stick to them.

[MinelabMan]

We have those like the one in the pic on the upper left. We call them hot rocks, you'll get what sounds like a good signal and it will go away only to come and go. Once you dig it and run it past your coil you'll get a very scratchy and broken signal. Different detectors and different settings will give different signals on these.

Here's a brief description of Hot Rocks

[NVRick]

The two bottom ones look like; Magnetite, or Hematite.

You can call your local university and see if there is a geology department that can ID them for you.

The guy I spoke to about mine said there are genrally two types of meteroite, stoney and metal. Metal ones do not break or chip. Stony ones that break open mite have a dark (scorched) sink.

If a maginet sticks its magnetite,
If not it could be hematite.

Both common in the west.

The red one is very interesting for sure.

Hope it helps

Rick

[dewcon]

I agree with magnitite. Most detectors work on Conductive which cause wrap around from the mineral content in the rock. Also, check your discriminate... you may have it too high and its nulling. I open my disc up (SE) to just above mineral sounds which eliminate those hot rocks. There are also COLD rock which just dont give a tone.

[bill(de)]

Curious on which detector your using as some detectors will Null on iron and the Minelab Sovereign is one that comes to mind. HH Bill

[digdan]

Originally Posted by bill(de)

Curious on which detector your using as some detectors will Null on iron and the Minelab Sovereign is one that comes to mind. HH Bill

Tesoro Vaquero, I should put it in my sig. But I've noticed the Vaquero works in a very special(as far as I know) way. Either the tone will build up (get louder), or build down (get quieter). Standard tones do not have a volume change. While negative responses start loud and quite. Positive responses start soft and get loud. Since it is a VLF I must keep it moving, but it does have great depth and accuracy.

I tune the MD buy "pumping" it against the ground and reading if its giving a "building up", or "building down" response. Once it gives me nothing, or just a simple tone, I know I'm tuned to the minerals in the ground(threshold adjustment aside). A Null(object found, but being discriminated) response is a quick flicker sound, almost like a very quick scratch on a old vinyl record.

Some of these rocks gave a "building down" tone, which I've never heard before from an object. I ussually get a building up, or if I'm discriminating, a Null, or a Building Up.

On these objects, I was not discriminating, and they gave me either the null, or negative (build down) response. Thus I call them Negative, or Null Rocks.