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In a recent question, 'Could an EVA Suit meant for Mars be used for EVA on another celestial, or vice-versa?', there was some discussion in the comments about the effects of a dust storm on Mars versus sandstorms on Earth.
Mars' atmosphere is much thinner, its gravity is lower but wind speeds can be quite high. How do these factors combine? Would a Mars dust storm be abrasive?

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According to the Mars-One webpage What are the risks of dust and sand on Mars?, that even though the wind speeds of the dust storms can be quite high - hurricane force, due to the far thinner atmosphere (1% of Earth), it would feel like a slight breeze.

Mars is dusty, with dust storms that can cover the planet (rarely), and

Airborne dust on Mars is about as fine as cigarette smoke. Particle abrasion will be limited due to the small size of the particles.

There is another side effect of a dust storm, particularly, a large one, is that, according to the NASA page The Perfect Dust Storm Strikes Mars causes significant atmospheric heating (up to 80F) - so thermal effects need to be considered.

The fine dust in the storms will pose another problem according to Future Mars Explorers Face Dusty Challenges (Mosher, 2007), is that it would electrostatically attach to everything, with

"If you walk through, pick up or simply touch the dust, it would gather charge and stick to you. We've already seen this on the rovers' wheels," said Geoffrey Landis, a physicist with the NASA Glenn Research Center in Cleveland, Ohio. "Things get even more interesting when winds come by and separate the charge."

and that, as the air is dry on Mars, the charge can build and potentially arc, damaging sensitive electronics if not properly shielded.

But more information and studies would be needed to fully determine the effects of the Martian dust.

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Part of this is also discussed in the How can Mars have dust storms with such a thin atmosphere? thread, but yes it would be abrasive, and direct evidence for this can be appreciated in all kinds of aeolian formations on the Martian surface, like the dunes of the Nili Patera region or the ones in the Lyot Crater, just to name a few of the most well know examples:

    enter image description here

    High detail HiRISE image of the Lyot Crater dunes on the move due to aeolian processes (Source: HiRISE / University of Arizona)

Now, while the atmospheric pressure and gravity are lower than on the surface of the Earth, and dust particles being on average lighter because of the lack of humidity preventing them from sticking grain to grain and forming larger dust particles, they would also be (for this same reason) finer grain and sharper. Not as sharp as the regolith dust on the surface of the Moon, since there is obviously still weather on the surface of Mars that would help polish these grains to rounder spheres, but still a lot sharper than the dust we mostly deal with on Earth. Because of the lack of humidity, the size of these dust particles would be as small as the size of crystalline structures of various rock salts, and those tend to be fairly sharp. On top of that, wind gusts of 500 to 600 km/hr (or 300-375 miles/hr) have been recorded by Mariner 9 and later orbited spacecraft, probes, landers and rovers, with typical wind speeds in the Martian atmosphere exceeding 200 km/hr (or 125 miles/hr).

So while you'd think that Martian dust would have less kinetic potential due to it being smaller, finer grain and the smaller gravity making them additionally lighter, the dust storms can be quite abrasive even if it would feel like you're in the middle of a mild breeze with merely visibility sharply decreasing. Some of this dust could also have corrosive properties in contact with different materials the space suit would be made of, with the dust being of all kinds of chemical compositions, originating either from Martian own bedrock erosion, silicate minerals and other dust of magmatic origins from its calderas, or even imported to Martian surface by impacted asteroids. For example, the Phoenix lander has found evidence of perchlorate, but other, more corrosive chemicals are not excluded with such low water vapor content of Martian atmosphere. And Martian storms also produce lightnings, another hazard that means they would be best avoided, and perhaps needless to say, visibility would be near zero, so even easier to lose footing or worse.

On top of that, the dust would tend to cling on the space suit (or perhaps better said environmental suit) not unlike the Lunar dust did on Apollo missions due to it being electrostatically charged or even magnetic (also discussed here), and its sharpness could lead to it lodging deep into the suit's fabric and causing triboelectric charge (small electric charge carrying particles rubbing against each other, for example the iron oxide, or rust, that can be found in top layers of Martian soil) or tearing the fabric by increasing suit's local friction, so pioneers on Mars will have to find ways to mitigate this dust problem. Using many layers and threading could help mitigate this and increase their durability, but with increased thickness and with it its surface, all these problems increase too, so any environmental suits used on Mars will likely be custom fit and skin-tight, perhaps like this BioSuit.

Additional hazard with longer exposure to Martian environment comes on removing the suit after entering a protected environment, with the tiny and sharp silicate dust posing health risk to humans, if it enters their lungs, causing silicosis, among other health problems.

So TL;DR - Martian dust storms would be best avoided, and they're hardly harmless even if their force isn't such to throw you off your feet if you found yourself in the middle of it.

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