File:Lapis Eyes Limestone (Rio Tascadero Limestone, Lower Cretaceous; Flor de los Andes Mine, Andes Mountains, Chile) (14802928794).jpg

"Lapis Eyes Limestone" from Chile.

In the commercial decorative stone trade, “marble” is used to refer to a wide variety of relatively soft rocks (H = 3 to 5) that will take a fine polish. These include true marbles and rocks that aren’t marbles, such as limestones, tectonic breccias, and serpentinites. True limestones are calcitic biogenic and ~chemical sedimentary rocks.

"Lapis Eyes Limestone" is a lazuritic-pyritic fossiliferous limestone from the famous Flor de los Andes Lapis Lazuli Deposit in central Chile. The gray material that makes up the bulk of this rock is marine fossiliferous limestone of Early Cretaceous age.

These rocks were metamorphosed twice during the Tertiary: 1) contact metamorphism by intrusion of monzogranites of the Río Las Cuevas Granite (late Late Oligocene, 24 Ma); 2) sulfur-metasomatism by intrusion of dacites and rhyodacties of the Portezuelo del Azufre Intrusion (late Middle Miocene to Late Miocene, 9-13 Ma).

Neither of these metamorphic events has converted the limestone to marble. The sulfur-metasomatism event resulted in the formation of blue-colored lazurite and brassy-gold pyrite (= most of the very dark gray spots in the above photo). Lazurite is a rare metamorphic mineral ((Na,Ca)8(AlSiO4)6(SO4,S,Cl)2). Rock-forming lazurite occurs at this locality - lapis lazuli. Afghanistan’s Hindu Kush Mountains are famous for having the highest-quality lapis lazuli on Earth, but the Chilean deposit also has high-quality material. The perceived lower-quality material is cut & polished into decorative stone, like this sample.

Stratigraphy & age of host limestone: Río Tascadero Limestone, Berriasian Stage to possibly Barremian Stage, lower Lower Cretaceous