Hornsilika

Hornsilika is a term that appears in some regional geological literature to describe a silica-rich material associated with hornblende-bearing rocks. It is not a formally recognized mineral species in major databases, and there is no universal definition. In usages where it appears, hornsilika denotes silica phases (predominantly SiO2) that occur interstitially in or as veins within hornblende-bearing rocks, or as microcrystalline silica replacing feldspar grains.

The composition is variable, commonly interpreted as microcrystalline quartz or amorphous silica (opal- or chalcedony-like) with minor impurities.

Occurrences are reported in granitoid, metamorphic, and volcaniclastic settings where silica saturation or hydrothermal alteration accompanies hornblende-rich assemblages. As a material, hornsilika is not a separate mineral; rather, it describes a textural occurrence of silica within a rock.

Property and identification notes: silica-rich phases are generally hard and with a vitreous luster; if crystalline quartz, hardness up to 7; if amorphous, somewhat softer. Identification relies on analyses such as X-ray diffraction to detect quartz or opal, and electron microscopy with energy-dispersive spectroscopy to confirm Si and O.

In geology, hornsilika is a descriptive term rather than a defined mineral, and its exact interpretation may vary between authors.

See also: quartz, chalcedony, opal, hornblende, hornblende-bearing rocks.