What is this optical component made of??

[rimshot]

Hi,
   I salvaged some parts (optical & electronic) off a chemistry
analyzer that was going to be scraped. The analyzer was a 
Toshiba medical system.
  The part in question is the mirror used to relay the light source
via fiber-optics to the cuvette with the analyte in it. Another mirror
relays the transmittance or absorption of the light source to the 
detector. The mirror is a small oval inside a clear cube.It is similar
to a cube beamsplitter(2 right-angle prisms cemented @ their hypotuse
faces), but small -- 10mm x 7mm x13mm.
  Anyone  know what  these are made of? Quartz,glass, or plastic?


		Thanks, rimshot at worldnet.att.net