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I'm hoping others can help me identify this odd looking hollow rock/mineral/metal thing. I'll give pictures, then a video, then some other helpful info.

First, here are some pictures. It's roughly 10 cm long: 10 cm long

Notice it's hollow parallel to the long axis: hollow inside

I took a hammer to part of the end to expose a new internal surface: inside end

The streak is reddish. I'm colorblind, so can't give more info, but I can provide a photo. The center streaks are from the unknown rock. The upper ones are from sulphur and the lower ones are from pyrite: streak color

The outer surface is interesting. It's spiral-like. Here's a video that shows the overall shape a bit better than pictures can:

Here's additional useful info.

Specific gravity (measured by me): Somewhere between 3.30 and 3.46. Upon exposing a new surface, I noticed a few air pockets. You can see them in the photo above if you look closely. No idea how much this decreases the S.G. measurement.

Location found: On the surface of a currently-empty stream bed. (It's been a dry summer.) The stream is in a wooded area in McCollum Park in Everett, WA. However, there is casual foot traffic from the city, so it's not necessarily a native rock. Could have been brought in. There are also buildings nearby.

Other useless info about discovery: The hollow inside part was full of some dirt and fibrous material.

Magnetic interactions: Attracted to magnet.

Mohs Hardness: Somewhere between 4 and 6 I think. It's rather brittle, so I find it difficult to do the test definitively.

Similar to: Looks very similar to my hand sample of "magnetite". The S.G. is all wrong to be pure magnetite (I'm new to this, bear with me), but it's still pretty similar to my sample.

Beyond knowing what the mineral actually is, I'd like to learn the process of how such a strange shape can be formed. Crossing my fingers for a natural explanation rather than some artificial building/construction explanation.

Thanks!

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  • $\begingroup$ My first idea upon seeing the title was a water pipe... $\endgroup$ – John Dvorak Sep 1 '18 at 1:23
  • $\begingroup$ Oh! had no idea rust could do that. $\endgroup$ – BMS Sep 1 '18 at 1:28
  • $\begingroup$ A waste (sewage) pipe, I would guess. In addition to rust, corrosion from H2S gas, scale from hard water and whatever sticks to the resulting rough surface. Some images here. Brings back not-so-fond memories. $\endgroup$ – Keith McClary Sep 1 '18 at 2:21
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This is a rusty pipe of some sort. Not a rock. You'd be surprised how messed up man-made iron materials end up looking after not too long in the natural environment, especially in a stream.

It's magnetic because it still have metallic iron in there, and also possibly some magnetite. The rest of it looks remarkably like rust.

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    $\begingroup$ Pretty sure it is wire rope perhaps previously used in forestry applications for high lead logging or as a main line from a skidder. The spirals on the outside would be the twist on the wire rope. The pattern on the end view is likely one of the major strands showing the individual strands. Wire rope often has a core made of different material so seeing it hollowed out is not unusual. $\endgroup$ – Friddy Sep 10 '18 at 23:20
  • $\begingroup$ @Friddy if it was rope cored AKA fiber cored that would explain why it is hollow. $\endgroup$ – John Jan 17 at 23:04
  • $\begingroup$ Depending on the age of the rope the fiber core would have been made with natural materials such as manila or hemp. In the soil this material would have rotted out once the oils dissipated out of the wire rope. Now these ropes are typically made with synthetic cores. Fiber core wires ropes are still extensively used, lexcocable.com/6x19-class-bright-galv. $\endgroup$ – Friddy Jan 18 at 0:12

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