Part One: Gravity-Related
First, the last sentence of the question asks for glass rain on a planet that humans can land on. But the rest of the question asks for a planet which would be in parts habitable for humans. There is a big difference between a world haBitable for humans and one which humans can land on and even take off from alive, as any astronaut who has ever been to the Moon can tell you.
Leaving aside the question of the temperatures, would the world as described be habitable for humans?
The nice-to-have section includes:
In the human-comfortable temperature region, the surface gravity does not exceed 2g.
In Habitable Planets for Man, 1964, Stephen H. Dole discusses the requirements for a world to be habitable.
Dole discusses the human gravity requirements on pages 11-13. Doles says that there was no evidence of a minimum gravity requirement then - now there is much evidence that extended stays in microgravity have bad effects on human health, and nobody know what the lower gravity limit will be yet.
For the upper gravity limit, Dole discusses experiments with men in centrifuges. Men with suitable support and in the correct postures can endure a few gs for short times. Men can also walk and move and manipulate objects in higher gravity than 1 g.
Tests showed that the time it took to complete various task increased with increased gravity, and that the times became quite excessive over 2 g.
Dole doubted that humans would ever want to colonize a world with a surface gravity over 1.25 or 1.5 g.
There are several ways you can react to this info:
Dig up research that indicates that humans would be willing to colonize a 2 g planet because its effects are not as bad as was thought when Dole wrote.
Decide that the surface gravity in the human habitable parts of the planet will be no more than 1.25 g or 1.5 g.
I note that will result in the surface gravity at the equator being somewhat less than at the human habitable regions. Which may or may not matter much if nobody ever goes to the equator.
As I just stated, if you go with a disc-shaped planet, a mini-Mesklin, the surface gravity will vary with latitude. And so will the escape velocity, I think. And unfortunately for science fiction writers, surface gravity and escape velocity do not increase or decrease at the same rate but need to be calculated separately. And the escape velocity is important for the planet's ability to retain an atmosphere for long enough for the planet to become habitable for humans.
On pages 34 to 35, Dole discusses the relationship between escape velocity and atmospheric retention.
You may also need to calculate the orbital velocity at the equator of your planet design.
You may decide that the human colonists are descended from many generations of humans who colonized planets with higher and higher surface gravities, thus becoming conditioned to survive and be happy in higher gravity than humans from Earth could.
Or maybe the colonists on your planet have been genetically modified to have greater tolerance for high gravity than unmodified humans.
Maybe the colonists on your planet use anti-gravity to make their buildings and settlements comfortable and healthy, and maybe they use anti-gravity vehicles and wear anti-gravity belts when exploring or working outdoors.
Or maybe the humans have colonized another world in the system with a lower gravity, and only come to your high gravity planet to take rich tourists for short visits that don't endanger their health. Maybe the tourists come to the planet to hunt exotic creatures, or to see a great natural wonder, or to experience the glass rain, or for some other reason. And possibly a discovery that the visits to the planet of grass rain actually involve too long exposure to the high gravity and are endangering people's health could be a plot point.
Part Two: Rapid Rotation.
The planet Earth has an equatorial radius of 6,378.137 kilometers and an equatorial circumference of 40,075.017 kilometers. Since it rotates once a day, once in 24 hours of 3,600 seconds, or once in 86,400 seconds, mater on the Earth's equatorial surface has a rotational speed of 0.4638312 kilometers per second.
Actually 24 hours is the synodic day of the Earth, the time it takes to rotate 360 degrees with respect to the Sun. That is slighty longer than the sidereal day, the time it takes the Earth to complete one physical rotation with respect ot the stars, and the time period which causes the equator to bulge slightly.
The sidereal rotation period of the Earth is about 23 hours (3,600 seconds each), 56 minutes (60 seconds each), and 4.100 seconds long. So it is 82,800 seconds plus 3,360 seconds plus 4.100 seconds. Or 86,164.1 seconds. So material at the surface of Earth's equator travels at a speed of 0.465101 kilomters per second.
Imagine a planet which has twice the equatorial radius and circumference of Earth, and has the same sidereal rotation period. It will have an equatorial surface rotation period of 0.930202 kilometers per second.
A planet which has three times the equatorial radius with the same rotation period as Earth will have an equatorial surface speed of 1.395306 kilometers per second.
A planet which has four times the equatorial radius with the same rotation period as Earth will have an equatorial surface speed of 1.860404 kilometers per second.
And so on.
So imagine planets which have the same equatorial radius as Earth but rotate faster that Earth's equatorial surface speed of 0.465101 kilomters per second.
A planet rotating twice as fast in half a sidereal rotation period will have an equatorial surface speed of 0.930202 kilometers per second.
A planet rotating three times as fast in 1/3 of a sidereal rotation period will have an equatorial surface speed of 1.395303 kilometers per second.
A planet rotating four times as fast in 1/4 of a sidereal rotation period will have an equatorial surface speed of 1.86040404 kilometers per second.
A planet rotating five times as fast in 1/5 of a sidereal rotation period will have an equatorial surface speed of 2.325505 kilometers per second. It will rotate once in 17,230.82 seconds, 4.78 hours.
A planet rotating ten times as fast in 1/10 a sidereal rotation period will have an equatorial surface speed of 4.65101 kilometers per second. It will rotate once in 8,615.41 seconds, 2.393 hours.
A planet rotating fifteen times as fast in 1/15 of a sidereal rotation period will have an equatorial surface speed of 6.97515 kilometers per second. It will rotate once in 5,744.27 seconds, 1.596 hours.
A planet rotating twenty times as fast in 1/20 of a sidereal rotation period will have an equatorial surface speed of 9.30202 kilometers per second. It will rotate once in 4,308.205 seconds, 4.78 hours.
Of course planets roatating that fast will becomemoreoblate, so Earth mass planets with those rotation rates would have larger equatorial diameters and thus would have faster rotational speeds on their equatorial surfaces.
Dole discusses the oblateness of rotating planets on pages 41 to 46. And from his discussion it would seem that it would probabily be difficult for a planet to stay intact with a high degree of oblateness due to rotation.
Dole, on pages 58 to 61, discussed the effects of rotation rates on planetary habitability. If the planet rotated too slowly, the long days and long nights would get too hot and too cold, and plants might die from lack of sunlight during the long nights. Dole decided that a rotation period of 96 hours (4 Earth days), would be about the maximum length consistent with habitability.
And Dole said that if a planet rotated too rapidly its surface gravity would fall to zero at the equator or it would become unstable.
If rotation rate were increased steadily, a limiting point would be reached when surface gravity at the equator fell to zero and matter was lost from the planet, or when the shape of the surface became unstable and axial symmetry was lost.
Just what extremes of rotation rate are compatible with habitability is difficult to say. These extremes, however, might be estimated at, say, 96 hours (4 Earth days) per revolution at the lower end of the scale and 2 to 3 hours per revolution at the upper end, or at angular velocities where the shape becomes unstable due to high rotation rate.
Earth has an equatorial radius of 6,378.137 kilometers. According to this orbital calculator, a satellite of Earth 6,378.14 kilometers from the center, or 0 kilometers above the equator, would have an orbital period of 1 hour 24 minutes and an orbital velocity of 7.9053 kilometers per second (km/s).
A satellite at twice that distance, would have an orbital speed of 5.5899 km/s and an orbital period of 3 hours 58 minutes.
A satellite at 3 times that distance would have an orbital speed of 4.5641 km/s and an orbital priod of 7 hours 19 hours minutes.
A satellite at 4 times that distance would have an orbital speed of 3.9526 km/s and an orbital priod of 11 hours 15 minutes.
A satellite at 5 times that distance would have an orbital speed of 35353 km/s and an orbital priod of 15 hours 44 minutes.
A satellite at 10 times that distance would have an orbital speed of 2.4998 km/s and an orbital priod of 44 hours 31 minutes.
A satellite at 15 times that distance would have an orbital speed of 2.411 km/s and an orbital priod of 81 hours 48 minutes.
A satellite at 20 times that distance would have an orbital speed of 1.7676 km/s and an orbital priod of 125 hours 56 minutes.
So if a world with the mass of the Earth has a diameter too many times larger than Earth's and rotates with the same period as Earth, material at the equator surface will have will have a surface velocity greater than orbital velocity and will move to a higher orbit, leaving the surface of the planet.
And if a world with the mass of the Earth has the same diameter as Earth but rotates too many times faster than Earth, material at the equator surface will have will have a surface velocity greater than orbital velocity and will move to a higher orbit, leaving the surface of the planet.
Thus there are limits to how fast a planet with the mass of Earth can rotate,and how oblate it can become, before it starts to break up.
Of course a way around that is to increase the mass of the planet to give it a higher orbital velocity at different distances from the center, thus making the orbital velocity higher than the equatorial surface speed.
But there are limits to how much you can increase the mass of the planet, without increasing the surface gravity and having other bad effects.
For example, plate tectonics, and a magnetosphere generated by an liquid interal region of the world, are considered to be desirable for the habitability of a planet.
This article suggests that the mass of a world determines whether it can have those desirable features.
On page 20:
A minimum mass of an exomoon is required to drive a
magnetic shield on a billion-year timescale (MsT0.1M4;
Tachinami et al., 2011); to sustain a substantial, long-lived
atmosphere (MsT0.12M4; Williams et al., 1997; Kaltenegger,
2000); and to drive tectonic activity (MsT0.23M4; Williams
et al., 1997), which is necessary to maintain plate tectonics
and to support the carbon-silicate cycle. Weak internal dynamos have been detected in Mercury and Ganymede
(Gurnett et al., 1996; Kivelson et al., 1996), suggesting that
satellite masses > 0.25M4 will be adequate for considerations
of exomoon habitability. This lower limit, however, is not a
fixed number. Further sources of energy—such as radiogenic
and tidal heating, and the effect of a moon’s composition and
structure—can alter the limit in either direction. An upper
mass limit is given by the fact that increasing mass leads to
high pressures in the planet’s interior, which will increase the
mantle viscosity and depress heat transfer throughout the
mantle as well as in the core. Above a critical mass, the dynamo is strongly suppressed and becomes too weak to
generate a magnetic field or sustain plate tectonics. This
maximum mass can be placed around 2M4 (Gaidos et al.,
2010; Noack and Breuer, 2011; Stamenkovic´ et al., 2011).
Summing up these conditions, we expect approximately
Earth-mass moons to be habitable, and these objects could be
detectable with the newly started Hunt for Exomoons with
Kepler (HEK) project (Kipping et al., 2012).
This suggests that the upper mass of a habitable world should be about 2.0 Earth mass.
Their sources are:
Gaidos, E., Conrad, C.P., Manga, M., and Hernlund, J. (2010)
Thermodynamics limits on magnetodynamos in rocky exoplanets. Astrophys J 718:596–609.
Noack, L. and Breuer, D. (2011) Plate tectonics on Earth-like
planets [EPSC-DPS2011-890]. In EPSC-DPS Joint Meeting 2011,
European Planetary Science Congress and Division for Planetary Sciences of the American Astronomical Society. Available
online at http://meetings.copernicus.org/epsc-dps2011.
Stamenkovic´, V., Breuer, D., and Spohn, T. (2011) Thermal and
transport properties of mantle rock at high pressure: applications to super-Earths. Icarus 216:572–596.
And a rocky planet with too much mass will have a high enough escape volocity to reain large amounts of helium or even hydrogen,thus becoming a gas giant. The tremendous pressures and temperatures at the cores of gas giants mean that they have no solid surfaces to stand on.
Part Three: Suggestions
One) Perhaps your planet has or had several small moons. A collison of moons might have turned them into lava, which is sort of a glass. The molten lave would gradually cool and solidify into amoon of pumice. Then another collison with another moon could have shattered the pumice moon into a ring. Particles of different masses might move to different distances from the planet, and collisons between particles might result either in them clumping together into larger pieces, or shattering into smaller pieces.
And perhaps tidal interactions with the planet, the star, other ring particles, and any surviving moons, might cause ring articles of the correct size to spiril in toward the planet and eventually fall onto the surface in showers.
It is speculated that falling ring material might have created the equatorial ridge on Iapetus, a moon of Saturn.
However, the creation of the ring would proabably have happened early in the history of theplanet, before it was capable of supporting advanced oxygen breathing lifeforms. And the ring system would proably only last for a few tens or hundreds of millions of years, so the planet would probably still not be habitable for advanced lifeforms by the time the ring system was gone.
Maybe the collisons and formation of the ring system happened unusually late in the history of the solar system, when the planet was already habitable. Or maybe it happened when the planet was young, but an advanced civilizaiton terraformed the planet to make it habitable billions of years before it otherwise would have become habitable.
An example of cyrovulcanism is on Triton, the large moon of Neptune.
The Voyager 2 probe observed in 1989 a handful of geyser-like eruptions of nitrogen gas and entrained dust from beneath the surface of Triton in plumes up to 8 km high. Triton is thus, along with Earth, Io, Europa and Enceladus, one of the few bodies in the Solar System on which active eruptions of some sort have been observed. The best-observed examples are named Hili and Mahilani (after a Zulu water sprite and a Tongan sea spirit, respectively).
All the geysers observed were located between 50° and 57°S, the part of Triton's surface close to the subsolar point. This indicates that solar heating, although very weak at Triton's great distance from the Sun, plays a crucial role. It is thought that the surface of Triton probably consists of a translucent layer of frozen nitrogen overlying a darker substrate, which creates a kind of "solid greenhouse effect". Solar radiation passes through the thin surface ice sheet, slowly heating and vaporizing subsurface nitrogen until enough gas pressure accumulates for it to erupt through the crust. A temperature increase of just 4 K above the ambient surface temperature of 37 K could drive eruptions to the heights observed. Although commonly termed "cryovolcanic", this nitrogen plume activity is distinct from Triton's larger scale cryovolcanic eruptions, as well as volcanic processes on other worlds, which are powered by internal heat. CO2 geysers on Mars are thought to erupt from its south polar cap each spring in the same way as Triton's geysers.
Turbulence at Triton's surface creates a troposphere (a "weather region") rising to an altitude of 8 km. Streaks on Triton's surface left by geyser plumes suggest that the troposphere is driven by seasonal winds capable of moving material of over a micrometre in size.
So the winds in Triton's ultra thin atmosphere are capable of moving tiny particles in the pluse of vapor from the geysers.
Suppose that your planet has a lot of icey materials and lots of mineral glass from volcanic eruptions, asteroid impacts, or whatever, mixed in with the ices. Internal heat and heat from the star may melt a lot of ices into liquids and evaporate them into gases. When gas pressure builds up too high, the gases will burst up through the ices and enter the atmosphere, carrying small particles of glass with them.
The glass dust might later rain down in various locations. if the glass is the same size as the dust that water drops form around, it might be the nucleus of actual rain drops which rain down. I don't know if the rainwater would have to be deglassified before it was safe to drink.
But how can there be cyrovulcanism on a planet that is as warm as Earth?
I personally, have observed patches of ice over liquid water just a few days ago. The dog I was walking sat down in one, cracking the ice so it could wallow in the mud.
There is lots of permanent ice on Earth,an d much more seasonalice. And during glacial periods there was more ice.
Possibly if the planet has long enough days, most of the ice in equatorial regions might sublimate into water vapor during the long days. During the long nights, most of the water vapor becomes liquid water and dew, and then ice forms over the liquid water. In the morning the sun warms up the trapped water mixed with glass dust udner the ice, and water vapor builds up until it erupts in gyesers, carrying much glass dust with it. The rain of water and glass dust might happen soon after sunset.
So those are my suggestions.