bluestone

/B L UW1 S T OW0 N/
noun
  1. 1

    Any of several bluish grey varieties of stone used for construction:

  2. 2

    Either of two related copper- and sulfur-based bright blue stones:

  3. 3

    Lapis lazuli, or its core constituent, lazurite.

Source: https://en.wiktionary.org/wiki/bluestone