Sometimes hyphenated: silico-calcareous.

The word "silvocalcáreo/a" occurs in Colombia's Estatuto Tributario Nacional art. 424: Bienes que no causan el impuesto, and in documents that quote it, but nowhere else.
http://estatuto.co/?e=710 (item 69.04.10.00.00)

"Silicocalcáreo", however, is a standard geological term and "ladrillos silicocalcáreos" certainly exist and can be found on the Internet. So I think it's very probably a typo in the actual statute.

It's not straightforward, however, because I can find no references to arcilla silicocalcárea or silicocalcareous clay. I think they intended to refer to silicocalcareous building materials but got it thoroughly muddled. I'm not sure how I'd deal with it in the translation, but a note is clearly called for.

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Note added at 5 hrs (2014-07-30 03:25:04 GMT)
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In other words, what I think you probably have to do is put "silvocalcareous clay", with a translator's note along these lines:

"The non-existent term silvocalcárea, in Article 424 of Colombia's Estatuto Tributario (item 69.04.10.00.00), is probably an error for silicocalcáreo, referring to silico-calcareous bricks."