TOWER HILL QUARRIES
near Monroe, Snohomish County, Washington, USA

LOCALITY IMAGES


GEOLOGY
Mount Persis Andesite - Tertiary. Hydrothermally altered andesite, varying in color from gray (less altered) to yellow, red and brown where heavily altered. Voids created by faulting and brecciation have been partially/completely filled by hydrothermal mineralization.

During the Summer of 2019, the first Washington occurrence of melanophlogite (pseudomorphed to chalcedony) was identified in the Tower Hill area near Monroe by mineral collector, Nick Carlson. Although the material had been collected for years prior, it was mistaken for chalcedony casts of calcite and overlooked. After the quarry was blasted again in 2020, single cubes and complex intergrown cubes were found in the quarry tailings. Since the 2020 blast, collectors have found it increasingly difficult to find new specimens. The Tower Hill area has three quarries that are owned and operated by the Washington State Department of Natural Resourcers (DNR). Please contact the DNR for the current collecting status.

MINERALS
*Calcite-
CaCO3 - Occurs as sharp, clear to opaque flattened rhombohedral crystals up to about one inch, similar to the calcite crystals that have been found at the neigboring Cadman High Rock Quarry.
*Quartz-
SiO2 - Occurs as chalcedony (blue, white, brown, colorless) in veins up to about 12-inches thick with some smaller veins consisting of banded light blue agate. Crystalline quartz is also present, with some crystals showing zoned, light-colored amethyst terminations. The most notable quartz occurence are the chalcedony pseudomorphs after melanophlogite [46SiO2 6(N2,CO2) 2(CH4,N2)] in open cavities within the chalcedony veins. The individual pseudomorphs show cubic morphology, occuring as crust-like aggregates (most common), sharp cubes (some isolated on the matrix) and complex intergrown cubes showing a stepped repeating pattern on the cube faces. The pseudomorphs range in color from blue to white to colorless and range in size from about 1 to 8 mm.

* photographed
 
QUARTZ (Var: Chalcedony) pseudomorph after
MELANOPHLOGITE

Photo Copyright Nick Carlson 2024

 
QUARTZ (Var: Chalcedony) pseudomorph after
MELANOPHLOGITE

Photo Copyright Nick Carlson 2024

 
CALCITE (flattened rhombohedra)
Photo Copyright Nick Carlson 2024

 
QUARTZ (Var: Chalcedony)
Photo Copyright Nick Carlson 2024