Reply by Dr Ted Nield (Editor, Geoscientist)
Thank you for your recent inquiry which has been passed to me for a reply. We receive many inquiries here and they are often about strange stones found in gardens (as a rule) which seem very dense and the question always is "could this be a meteorite?" - and the answer is always "No". However in your case, and for the first time ever in my experience, I have to say that the answer could well be "yes"!
First, the stone you say is black - this is indicative that the outer fusion crust is still intact. This forms during passage through the atmosphere when the friction of the air melts the outermost layer of the meteorite. You do not mention if the black crust extends over all of the surface or just part; small meteorites like this are sometimes fragments of larger ones that explode high in the atmosphere from the physical stresses. In these cases it is not uncommon for the fusion crust to cover only part of the surface, and for other parts to be grey like concrete.
If it is a meteorite, it is probably a "stone" rather than an "iron". One that small reaching the ground would not have been travelling with cosmic velocity (which can be around 30 kilometres per second) as the atmosphere will have taken all that energy away (and converted it into heat - hence the fusion crust). By the time this one hit your car it would have been just a falling rock - falling under gravity alone, that is; but as it could have been falling for over 10km, and perhaps from space, this would have been at its terminal velocity in air, which at a high angle would be quite enough to punch a neat hole in your sunroof.
You should take it to your nearest geological museum together with a record of the time and place where it fell. Small meteorites are not usually hugely valuable, though value depends on rarity. To determine its lithological type, the key to determining its value, it will be necessary to have it examined by an expert.
However it is very likely that it is a type known as a "chondrite", a piece of the planetary nebula that failed to make it into a planetary body when the planets were accreting. It is probably therefore unaltered since 4567 million years ago, is older than any rock on Earth and the oldest solid object it is possible to hold in your hand.