SIGHTING REPORT UFO sighting at (North-East of) Amstelveen

To my perception: At first it looked like a bubbled black windshield (2 bubbles) or a flyer, or maybe even a pair of balloons. But balloons don't move in such an absurd manner (see below). The skie was VERY clear and bright. I saw the object from the 9th floor of my office building.
To my colleague's perception: The object was cone-like but as it was moving and turning it sometimes showed the shapes of a small rocket.
These perceptions are different, probably due to the large distance and the limited time of contact.

It zoomed constantly, almost within a straight line from where we watched it, moving toward and from us. Estimating the distance, this moving must have been at least a few hundred meters in only one or two seconds! By the end of the sighting, it spinned, changing color from black to silvery-shiny and it showed a small white halo just before it disappeared into the sky at an incredable speed.

We don't know what we've seen exactely but we are almost sure it wasn't something that belongs in our skies (like balloons -too far to be seen anyway- , planes -we're close to the airport, so we know what a plane looks like from ANY distance- or birds). If anyone has seen this object, I'd like to know more about the encounter. Contact me via email.