You are here:

Jewelry, Gems, & Minerals/What are these nodules?



They are fragile and can crumble, leaving little metallic needles. They appear to have some kind of sediment on the botryoidal surface. They were found in a jar from a very old lapidary/mineral collection. It has a strong not so good smelling odor when smelling in the jar. They are not attracted to a strong magnet. I was thinking maybe a cobalt crust nodule from the sea or some other type of manganese nodule perhaps? I found this photo searching around the web which is the closest thing I've seen so far other than pictures of manganese nodules.


Any information or opinions would be great, thanks.

- Jake

Hi Jake,
Thank you for your preliminary research. It does narrow the choices somewhat. While I can not be conclusive without the physical specimen, I might give you a few pointers.

Manganese nodules from the ocean floor contain a large amount of iron and can be attracted to a very strong (rare-earth) magnet. Try to flake off some slivers with a file and see if the small flakes are magnetic. Also, manganese nodules grow concentrically, like tree rings. If you bust one open and use a magnifying glass you should see indications of that growth.
However, there are other possibilities of minerals that a dark, or black with a botryoidal habit. I noticed in your picture that there are some indication of what looks like acicular (needle-like) crystals of same color on the surface of your specimen.

You could do some simple tests and get back to me for a better interpretation:

Does the black mineral scratch glass? Get a thick glass plate and drag your specimen across. You may have to lean into it with some force. Make sure you can feel a scratch with your fingernail and the mineral did not just leave a powder streak behind which will rub off. Does it scratch the glass easily, with difficulty or not at all?

A more sophisticated test would be to check the specific gravity (SG) of the mineral. You will need a clean chunk without and dirt, dust or mud coating it. Get one of those cheap hanging postal or fish scales. Tie the rock to a thin thread, hang from postal scale and weigh. This is called "weight in air" or Wa; record the measurement in grams (if in ounces then convert). Now submerse the hanging rock into a cup with water. Make sure your mineral does not touch side and bottom and is completely submersed (Of course, do not submerse the scale). Record this "weight in water" (Ww) also in grams. Calculate the density or specific gravity (SG) of the mineral as follows (make sure units are in grams):

SG = Wa / (Wa-Ww)

With the approximated Specific Gravity data a search can be performed in mineral data bases for a close fit. I have listed the SG and hardness of likely mineral candidates for your specific specimen:

Baddeleyite (ZrO2) (SG=5.8, will scratch glass); Cassiterite (SnO2) (SG~7, will scratch glass); Descloizite (Pb(Zn,Cu)(OH)(VO4)) (SG=6.2, will NOT scratch glass); Hematite (Fe2O3) (SG=5.2, may scratch glass with difficulty); Uraninite (UO2)(SG~11, may scratch glass with difficulty, radioactive: check with Geiger counter); Wurtzite (ZnS) (SG~4, will NOT scratch glass); Goethite (FeO(OH)) (SG=4.3, may scratch glass with great difficulty).
There might also be other possibilities.

If you want a full investigation of your specimen with report for free, you may want to consider our free mineral identification services from the Metropolitan State University of Denver as part of our community outreach. For details please see:

You do not have to send a pound heavy chunk. A few representative chips of the material would suffice.

Jewelry, Gems, & Minerals

All Answers

Answers by Expert:

Ask Experts


Uwe Richard Kackstaetter, Ph.D. (Dr.K)


I can answer questions concerning minerals, mineralogy, gems, metals, and anything that has to do with geology. However, I am NOT a jeweler. Questions about values, settings, gem stone cuts and appraisals are best directed to other experts on this site. I can however aide in the identification of unknown mineral materials. As a public service and part as training for new geoscientists, our university department provides FREE mineral identification for individuals. Please contact me for details or go to for details..


I am a professor of applied geology and mineralogy with many hours of field experience. Furthermore, I enjoy recreational gold prospecting and mineral collecting. As a professor I am engaged in research concerning minerals and their occurrence.

Member of the GPAA (Gold Prospectors Association of America) as well as the Association of Environmental Geochemists. Member of the GSA (Geologic Society of America) Member of the AIPG (American Institute of Professional Geologists)

Here is a small sampling: Mineral-rock handbook: Rapid-easy mineral-rock determination : written for anyone interested in minerals and rocks - Proctor, Peterson, and Kackstaetter;Macmillan Pub. Co. (New York and Toronto and New York) Physical Geology Laboratory e-Manual [CD-ROM], Kackstaetter, Earth Science Education LLC Colorado Front Range Self-guided Geology Field Trips, Kackstaetter,

Ph.D. in Applied Geology and Mineralogy. I am actively teaching courses in mineralogy and a variety of field courses with mineral collecting opportunities. Background in precious metal exploration.

Past/Present Clients

©2017 All rights reserved.