Possible micrometeorite isolated from roof debris collected from a Houston home in April 2017 (C) Daniel Friedman  S.R.Micrometeorites in Roof Dust/Debris
Find micro-meteorites in roof gutters?

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Micrometeorites from rooftops:

This article describes the collection and examination of debris and granules from an asphalt shingle roof in Houston TX. We conclude that it's not that easy to tease out a possible micrometeorite from a large volume of roof dust and debris, even when using a magnet.

Page top photo, a small hard sphere isolated from roof debris, attracted to a magnet, possibly a micrometeorite.

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Are the Magnetic Particles in Debris in Roof Gutters Micrometeorites?

Roof shingle debris in a Houston TX gutter - does this material include micrometeorites? (C)  SRQuestion: magnet picked up roof shingle granules in the gutters: are these micro meteorites?

I ran a magnet through a little pile of shingle granules in the gutters, and found metal particles and flakes. Are there metal flakes, or any metal at all in the granule protective layer of asphalt shingles? Must know before I lecture on meteorites. S.R. Houston TX 2017 03/05

I passed a magnet through a pile of granules in the gutter and found many flakes of metal. Are metal flakes part of the "mineral" coating? If not, I suspect meteorite particles. S.R. by private email 2017/11/02

[Click to enlarge any image]

Photo: granular debris in a plastic roof gutter of a home in Houston Texas.

Reply: probably not if there is nearby rusting iron or steel or if the particles are large

Is this the same dust we discussed back in April? I recall noting that the metals found in roof shingle granules are most-often copper, zinc, or sometimes aluminum in coatings, included for algae resistance, reflectivity, or appearance.

I'm not, however entirely surprised that you'd find magnetic or iron based particles. Magnetic particles in roof debris or dust could be from inclusions used to give an asphalt shingle a desired color or they might be from rusting metal such as that I see in one of your photos.

Asphalt roof shingle granules may include metallic components (C) InspectApedia SRHowever there are certainly going to be exceptions to what's common, and some magnetic metals including iron oxides might be used for color purposes, as I'll cite:

Photo: mineral-granule coated asphalt roof shingles on the Houston TX home.

Metallic Iron Oxides Used in Roof Colorings

Sources of both metallic iron oxides and other metals used in asphalt roof shingles or roll roofing that are coated with mineral granules include metal-flakes used to provide a desired color to the shingles (Hansen 1983 & Kiik 2002) and also metallic oxides used to increase the solar reflectance of roof surfaces (Levinson 2007).

Non-magnetic particles washing off of roofs and into gutters, onto the ground and into nearby waterways include minerals or metals used to improve the roof's resistance to algae growth and staining. The metallic component of asphalt roof shingle granules might contain copper or zinc - those are not magnetic minerals.

Examination of particles washing off of roofs, both mineral and others, is not new.

VanMetre and Mahler (2003) looked at the composition of particles and wash-off from rooftops and the contribution of these materials to contamination in urban streams.

Other Sources of Magnetic Particles in Roof Runoff: Metallic Rust Particles

Rusty metal roof components can be a source of magnetic particles in roof dust and debris - these are not micro meteorites (C) InspectApedia SR

Iron particles that may be attracted to a magnet could come from other roof sources such as metal chimney caps, flues, or plumbing vent pipes, even galvanized metal flashing- depending on the age and type of on-roof components at a building.

Photo: rusty metal roof flashing can be a source of iron and iron oxide that one might collect by magnet in roof granular or dust debris.

To separate metallic particles of rust from iron-rich micrometeorites you will need to use a high power magnifier or a stereo microscope for a first pass.

Properties of MicroMeteorite Particles vs Other Spherical Particulates

Genge et al (2017) writing in Geology, described micrometeorites as small, principally spherical particles that have been collected in small numbers from rooftops.

Backscattered electron microscopy images of the particles studied by those authors show that the particles are principally spherical, but never perfect spheres.

That helps to rapidly distinguish potential micrometeorites from very spherical particles seen under the light microscope and more-often identified as paint droplets or perhaps certain basidiomycetes or as certain pollen grains that may occur at similar sizes.

The Genge article is helpful in identifying micrometeorites as they note that

The identification of particles as micrometeorites is achieved on the basis of their compositions, mineralogies, and textures.

All particles are silicate-dominated (S type) cosmic spherules with subspherical shapes that form by melting during atmospheric entry and consist of quench crystals of magnesian olivine, relict crystals of forsterite, and iron-bearing olivine within glass. - Genge (2017)

The authors explain that because they are super-heated while passing through earth's atmosphere, those particles that are not incinerated are generally spherical in shape and are comprised of a range of minerals that they identified, including iron.

As I will cite below, an individual particle of cosmic dust that might be found on rooftops, while often magnetic, is also very small, in the 100u range up to 300-440u. (Buddhue 1950 & Handy 1953).

As a point of reference, individual ragweed pollen grains are about a tenth of that size. Human hair ranges in thickness from about 20u to 180u. Most human hair is around 25-100u in diameter.

Without a high power microscope you might have difficulty seeing such individual particles.

The presence of such dust particles on the earth's surface has been discussed in the U.S. since at least the 1950's, and such particles have been collected from deep sea sediment where it is possible to obtain samples that are not contaminated or confused by contemporary airborne particulates in the industrialized (and globally contaminated) world.

In March 2017 in the New York Times William Broad reported on flecks of extraterrestrial dust that might be collected from rooftops (Curiously not all of such tiny particles simply burn up while passing through the atmosphere, but they are heated to a very high temperature, probably explaining their spherical form when collected on earth).

That article is of interest and pertinent to your question since the dust particles were collected from gutter sediment. However nothing in that report mixes roof granules with cosmic dust. (Though I imagine that small dust particles would be mixed in with roof mineral granules and might even adhere to them.

I'd be surprised, however if the magnetic properties of the dust were strong enough to permit a magnet to lift up entire roof mineral granule particles).

I have some of your gutter debris sent to me back in April. I'm back in the U.S. and will take a look at that in our lab as soon as I am able, and I'll report to you on what I can see. I will look, particularly, for particles similar to those discussed in the Broad (2017).

It may be significant, however that the Geology article has not been cited by other scientific researchers - at least not in any online search I could perform as of November 2017. So further thought and reading and investigation are probably appropriate.

Reader Follow-up: roof dust micrometeorite experiment as school project

Roof shingle debris in a Houston TX gutter - does this material include micrometeorites? (C)  SRI conducted a little experiment after writing you last. I placed a strong magnet just above the shingles on my roof... no attraction. Then I scraped some of the granules off and tried the magnet... nothing.

But when I ran the magnet through some granules that had collected in the gutter, I get many, many small pieces of ferrous metal. This confirms something I read about the whole Earth being constantly bombarded by meteorites.

Most of them burn up in the atmosphere, but some survive as flakes and particles and land on rooftops (and on everything else, too). Imagine that -- being able to collect space material off your roof.

I've collected about an ounce of flakes and I'm going to give a lecture at my astronomy club on this subject on Friday. It will make an interesting school science project for kids. - S.R. 2017/03/05


Also, if you like, send me a dust sample in a clean ziplok freezer bag and when I return to the U.S. later this spring I'll examine it in our forensic lab.

Reader Follow-up:

I'll send you my samples and be as sterile as possible. I hope it survives in your in-box for that long. Please write upon your return.


As we're not so worried about biological particles, the sample should be ok in transit or storage.

Photos of your roof, closeup of shingles, and closer photo of the granule debris would be good to have too.

If you have access to a 100x or greater microscope you might take a look at the dust yourself as well. I work at 620 to 1200x and use polarized light, microchemistry and a few other tricks to take a closer look.

Reader follow-up:

Attached are the photos you requested. The first one is of a space between two lengths of gutter that didn't come together, leaving a convenient "trap" for particles.

The second is of places where the dips of the corrugated roof empty into the gutter.

I'm mailing a sampling of the particles I collected with a magnet. I'm anxious to see what your analysis comes up with. - S.R. 2017/04/04


Lab microscope and camera (C) Daniel FriedmanBetter to have a roof or gutter debris & dust sample collected physically without resorting to a magnet so that we have a representative sample not a magnetically-selected sample.

We can always separate magnetic particles in the lab.

I also note in your photos that roof runoff crosses what looks like galvanized metal flashing down onto a corrugated metal roof; it'd be no surprise to find some rust and other metallic fragments in roof runoff from such a roof.

Reader follow-up:

I just now mailed a second sampling of roof particles through which no magnet has been passed.

As for the flashing, I would imagine an analysis would distinguish rust from meteoric material but most-likely rust flakes and particles are visually obvious and will be obviously different from a particle that was superheated, melted, and became an ovoid particle passing through the atmosphere.

Later, when time permits, perhaps you or other readers will assist by collecting particles from other roofs with no obvious sources of extensive rusting metal.

And in answer to your query, yes a microscopist can usually recognize rust in the microscope, even without chemical testing. Rust fragments are, well, rust-colored, and tend to be irregular flakes and pitted irregular surfaces.

Meteoric material is more smooth and tends to be spherule-shaped though not likely perfect spheres.

Lab Photos of Roof Debris Screened for Evidence of Spherical Micrometeorites

Rust flakes found in roof debris from a Houston Texas roof gutter (C)

Above: Under the stereo microscope at low magnification metallic iron rust flakes were the dominant particle in the gutter debris sample collected using a magnet.

In the photo you'll also see a small quartz fragment, possibly from a mineral granule roof coating or from road dust and debris. You will also see very small sub-micron particulate debris, all irregularly shaped at this magnification.

[Click to enlarge any image]

The largest rust flake in its long-dimension was about 2mm.

Spherical particles mixed in roof debris from a Houston TX home (C) Daniel Friedman at

Above: magnified at about 720x we examine the smaller particles mixed in with the roof debris collected from the Houston TX home's roof gutter in 2017.

The smallest particles in this photo are about 1u in diameter. The two spherical particles are most-likely paint droplets. The sample is illuminated here by transmitted light.

Small spherical particle from Houston roof selected for closer examination vs micrometeorites (C) Daniel Friedman at

Above: we selected this tiny spherical particle (about 90u) for closer examination, but it's so round that I already suspect it's either a paint droplet or a bubble.

Top lit examination of the small spherical particle from the Houston rooftop (C) Daniel Friedman at

Above is the same spherical object, illuminated by top-lighting under the forensic microscope (POLAM) in our lab. The clear/white colour suggests that this is simply a bubble in the mounting fluid.

Bubble in mounting fluid at 1200x (C) Daniel Friedman

Above is the same spherical rooftop "object" magnified to about 1200x in oil immersion. It's a bubble, not a particle.

There might be micrometeorites in the debris sample from this Houston Texas roof but our first pass through the particles collected by a magnet didn't produce one.

Microscopic Photos of Granular Roof Particles Collected Without a Magnet

Mineral granules from a Texas roof (C) Daniel Friedman Mineral granules from a Texas roof (C) Daniel Friedman

Our photo above shows a first pass look at particles collected from the Houston roof gutter - clearly we're looking mostly at (mostly white) mineral particles - rocks or mineral granules.

Our second photo above shows some of these particles at higher magnification. These are not micrometeorites.

Next we focused our attention on smaller particles in this roof debris sample. In our top-lit microscope photo below we see four silver-colored spherical objects. Could those be micrometeorites?

Top lit closeup of small roof debris particles, possible micrometeorites (C) Daniel Friedman at

Possibly, but it's necessary to take a more-careful look. In many mounting fluids including Triacetin and simple immersion oil air bubbles can be quite small and under some light can look silver. Side lighting and top lighting can usually sort out this question.

Taking a Second Careful Look Through Roof Debris Particles: the search for micrometeorites

We repeated this experiment using immersion oil to secure our particles: in that mix were indeed some perfect silver spheres of tiny air bubbles.

Below I'm using a small magnet to transfer magnetic particles from a collection of roof debris particles onto a microscope slide whereon I've placed a drop of immersion oil.

When working with a stereo microscope we're not using a cover slip, but the immersion oil keeps me from accidentally blowing off or losing the particles en route to the microscope.

Using a magnet to sort through roof particles (C) Daniel Friedman

The blue grid lines in our earlier photos give a relative scale: each full square = 0.25" or about 6.35mm or 6350u (microns). So if we have a particle that's about 1/20th of a grid square in dimension we're looking at a 300u particle.

In the roof debris "micrometeorite search" sample above and enlarged below also saw large spheres of iron rust (shown below) as well as mineral granules, quartz, and fragments of asphalt.

Round sphere of iron rust from rooftop metal object (C) Daniel Friedman

Above, a comparatively large rough sphere of rusty metallic debris, probably from rusting metal flashing seen in roof photos earlier in this article. This is not a micrometeorite.

To screen roof dust and debris for micrometeorites that can be identified by simple light microscopy and without chemical analysis we looked for the following:

Probe separating large particles from roof debris to search for micrometeorites (C) Daniel Friedman

Really? This procedure will not identify all types of micrometeorites. That's because not all micrometeorites melt during their passage through the atmosphere, and thus some micrometeorites may appear to be irregular in shape and un-melted, coarse grained, crystalline and may vary in color: metallic, black, crystalline,(Genge 1997) (Maurette 1991) (Kurat 1994)

Using a small probe (shown at page top) to push aside the very large roof mineral granules we looked with care through the remaining debris and found this sphere, a hard metallic spherical object about in the photo below. We pushed this particle off more-or-less by itself for a closer look. This particle is about 100u in diameter.

Possible metallic micrometeorite collected from a roof gutter, Houston TX April 2017 (C) D Friedman

The spheroid particle shown above was wet and held in place by immersion oil and has other still-smaller debris fragments adhered to it. This might be a micrometeorite. But take care, Anselmo (2007) warns that most small spherical particles that you might collect from outdoor dust and debris are not micrometeorites.

These results suggest that it is not a trivial exercise to tease particles that may be micrometeorites out of a hand full of debris collected from a roof or roof gutter. Indeed, Larsen and Genge of Project Stardust in Oslo reported that

In order to separate the MMs from other types of terrestrial spherules, Project Stardust conducted ~1000 field searches for particles (~50-5,000µm in size) in ~50 countries worldwide over 7 years. (Larsen 2016).

Research on Microscopy & Analysis of Roof Granules, Dust, Debris for Particles of Interest


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