Rocks that set off metal detectors/pinpointers

[Bucket Lister]

Is there a list of rocks & minerals that will set off metal detectors?
I found such a stone today--it was infuriating!!!! 🤬

After several minutes of sifting through substrate with my pinpointer expecting to find another rusty square nail, all that was left was one stone. It doesn't set off the pinpointer like being in contact with a piece of metal, but it does set it off--like being a few inches away.

No, it's not being set off by my keys or pocket change--BT-DT. 😳

 

Amazon Forum Fav 👍

How to Research for Treasure Hunting and Metal Detecting From Lead Generation to Vetting - Grab it through Amazon!

[Midden-marauder]

Is that washer-tuning trick confined to Minelab pinpointers?

I haven't run into any brick yet that I can think of, but now that I know about hot & cold rocks (🤦🏼‍♂️), I'll keep it in mind.

In the back of my mind, I figured something like magnetite might do it (wasn't sure about hematite), but I don't run into either of those either.

No, all pinpointers can be super tuned, it's sometimes called the coin trick. I can give you details on how it works if ya like. I guess theoretically any non motion detector could be super tuned but usually it's only used with pinpointers to push them to the limit of depth. I only use the trick on some occasions, depends on what I'm hoping to find and where.
Funny thing happened today, funny coincidence: we were up hiking and we came across an area that I'm reasonably convinced is an abandoned camp ground that, based on context artifacts, probably operated from the 60s to the 80s. As I was poking around trying to nail down dates at the site I came across a hot rock, big one too. Bigger than my hand for sure. Based on the color of the rock I'm assuming it may be rich in iron, red hematite perhaps. It only triggers the pinpointer on one side but it is a bonafide, nature made hot rock! Even my cellphone magnetometer reacts to it

 

Amazon Forum Fav 👍

Family Maps of Hinds County, Mississippi, Deluxe Edition - Grab it through Amazon!

[Almy]

I find quite a few hot rocks in the river cobble. Most are dark and hard and some are brown sandstone. They usually give one strong ghost signal on each side as the detector swings over them, but sometimes just a single signal similar to a copper penny. None have been magnetic. I have not gotten a signal from any of them with my Garrett pinpointer.

 

[Bucket Lister]

I find quite a few hot rocks in the river cobble. Most are dark and hard and some are brown sandstone. They usually give one strong ghost signal on each side as the detector swings over them, but sometimes just a single signal similar to a copper penny. None have been magnetic. I have not gotten a signal from any of them with my Garrett pinpointer.

Huh. My pinpointer is the only way I find them.
Rarely a strong signal; more often, being in contact with one sounds like being several inches away from a valid target.

 

[Midden-marauder]

Huh. My pinpointer is the only way I find them.
Rarely a strong signal; more often, being in contact with one sounds like being several inches away from a valid target.

I think the increased sensitivity to tiny targets found in many pinpointers means they can pick up on some stuff the larger coils are essentially blind to. A tiny piece of iron won't set off my 9 1/2" coil but my pinpointer will sniff it out like a pro if it's within range. The bricks and now one hot rock that I bothered to take home probably contain only the smallest quantity of iron but it's just enough, just enough to set it off. In terms of the red brick I still say that's a potentially useful quality from an archaeology perspective, finding buried brick remnants is an important clue. As for the rest, well, I now collect hot rocks/magnetic rocks when I find ones worthy of comment. Makes for some unusual collecting!

 

[Bucket Lister]

I think the increased sensitivity to tiny targets found in many pinpointers means they can pick up on some stuff the larger coils are essentially blind to. A tiny piece of iron won't set off my 9 1/2" coil but my pinpointer will sniff it out like a pro if it's within range.

Adjusting the sensitivity on your coil doesn't help that?

My 9" coil is picking up everything. Sometimes it can be infuriating, but I have to laugh at myself all the same. I'll get a TID something like 90-94 that eventually turns out to be a ½" long fragment of a wire brad, or ½ cm² piece of foil, 10" deep.

Sometimes finding them in my hand with a pinpointer can be frustrating--almost like panning for gold I imagine, with all the back & forth, and material falling back into the hole.

 

[Midden-marauder]

Adjusting the sensitivity on your coil doesn't help that?

My 9" coil is picking up everything. Sometimes it can be infuriating, but I have to laugh at myself all the same. I'll get a TID something like 90-94 that eventually turns out to be a ½" long fragment of a wire brad, or ½ cm² piece of foil, 10" deep.

Sometimes finding them in my hand with a pinpointer can be frustrating--almost like panning for gold I imagine, with all the back & forth, and material falling back into the hole.

Ya know, in terms of my big coil I'm gonna upgrade before too long, getting into metal detecting was an experiment so I didn't pull for pricy stuff right off. The experiment ended up becoming passion so ya know but.....
I get, on my current coil, often at high sensitivity, a lot of high, 90+ VDI junk signals. Silver doesn't even appear to ring up so high on that machine, deep deep iron, pieces of god knows what at depth or right on the edge of detection range. Hot rocks I suspect, an aluminum can about 14" down perhaps, rusty bits of iron of possibly tiny size, pipes buried 12" down etc. etc. if it rings up over 90 on my machine it's a bit of a mystery and I don't dig those typically, they often report at 8"+ on my machine so they're either just beyond stable detection range or are super tiny just a couple inches down, nothing I want to find. It's a mystery on my big machine, adjusting sensitivity doesn't mean those 90+ signals go away, they just get more shallow or at least that's the assumption. They're trash targets, that's how trash targets show up on my machine. Yes I'm gonna buy a better one but for now that's what appears to be the case. No idea actually

 

[oldkoot]

The hot rock I found is much smaller--I would say less than two cubic inches--and just part of the topsoil.

It's got me thinking though... If someone were interested in actually hunting/collecting these hot rocks, a bank run gravel pit might be worth detecting.

You think one is frustrating you should detect an area that is covered in those little devils, thats what us Nugget hunters deal with all the time

 

[Bucket Lister]

You think one is frustrating you should detect an area that is covered in those little devils, thats what us Nugget hunters deal with all the time

That was just the first, and some time ago. Since then, I'm finding them fairly regularly. More common/dense near the (suspected) privy sites, but can be anywhere. The lightweight ones are graphite; heavier stones... (?)

Where I live & detect, I will NEVER have to worry about finding a nugget. 😉