I have a pair of Opus3 Credo speakers that are made of a composite of crushed marble and concrete. They are actually the same shape as yours. The crossover is housed in a bakelite plinth which is bonded to the bottom of the speaker. I've had them for 20+ years. They were manufactured for Opus3 which is a Swedish company. The company is still going strong, it specialises in producing high quality audiophile vinyl LP's.

The speakers themselves sound fantastic and compare well to my more modern B&W 685's. I use them exclusively for vinyl playback fed by my Linn LP12.

Here's a link to some ltd info about them if you're interested: http://www.audiocircuit.com/Home-Audio/Opus-3