Howardite: Rattlesnake Jasper

Howardite is an Opalised silicate with a distinctive interwoven and banded pattern and is noted for its rich golden yellow and pinkish-brown colors.

Howardite also known as "Rattlesnake Jasper" and “Royal Flamingo Jasper” is a rare form of opalized/silicate volcanic tuff from northern Nevada. It is a very unique and beautiful red to brown brecciated jasper interspersed with clear agate and/or opal.

Red Howardite from Nevada. Photo: SilverHill Lapidary/Jeffrey Hill

Howardite Formation

Originally volcanic tuff: Rattlesnake Jasper starts as volcanic tuff, a type of rock formed by the accumulation and compaction of volcanic ash and debris. This ash is ejected during volcanic eruptions and settles, forming layers over time.

Opalization: Groundwater rich in silica permeates the volcanic tuff, leading to the process of opalization. This process replaces the original minerals in the tuff with silica, resulting in the formation of opal and other silica minerals.

Brecciation: Subsequent geological events, such as tectonic movements, can cause the opalized tuff to fracture and break into fragments. These fragments are then cemented together with additional silica and other minerals, forming the characteristic brecciated texture of Rattlesnake Jasper.

Howardite Discovery 

The specific locality for Howardite appears to be unknown. Howardite is said to have been discovered in a small occurrence/pocket in the 1940's or 1950's, and the locality/deposit was thereafter said to be mined out, lost, or closed to entry for military purposes (depending on which account you hear). From what I have heard it was last dug in the 1970's and the discoverer could not find his way back to the deposit.

Rediscovered about 2015-2016 by dominion gems. Four claims were located on the deposit in january 2018 by dominion gems, but not recorded to keep the locality "Private" and to deter poaching and highgrading; shortly thereafter the deposit was rediscovered by others.

Rough Red Howardite from Nevada. Photo: SilverHill Lapidary/Jeffrey Hill

Occurrence

Rattlesnake Jasper is primarily found in the Velvet Mining District of Pershing County, Nevada.

It occurs as veins and breccia deposits within volcanic ash beds and is often associated with other minerals like quartz and calcite.

Due to its limited occurrence and unique beauty, Rattlesnake Jasper is considered a relatively rare and valuable gemstone.

Polished Red Howardite from Nevada. Photo: SilverHill Lapidary/Jeffrey Hill

Properties of Howardite

Composition: Primarily a blend of chalcedony (microcrystalline quartz) and opal, with additional trace minerals like iron oxides and manganese. Some sources also mention calcite and dolomite as minor components.

Color: Varies greatly, with a characteristic "brecciated" appearance featuring reddish-brown, yellow, orange, and white patterns often intermixed with clear agate or opal veins. The iron oxides are responsible for the red and brown hues.

Luster: Vitreous to waxy, depending on the specific mineral composition and texture. Areas with higher opal content may exhibit a more waxy luster.

Crystal System: Microcrystalline (no true crystal structure) due to its mixture of chalcedony and opal.

Streak: White, as expected from its quartz and opal composition.

Hardness: 5.5-6.5 on the Mohs scale, relatively hard and durable for a gemstone due to the presence of chalcedony.

Cleavage: None, as with most chalcedony and opal varieties.

Crystal Form: Massive, botryoidal, brecciated, or nodular. It rarely exhibits distinct crystal faces due to its microcrystalline nature.

Density: 2.2-2.4 g/cm³, slightly lighter than quartz (2.65 g/cm³) due to the presence of opal and other minerals.

Transparency: Translucent to opaque, depending on the density and presence of inclusions. Areas with higher opal content may be more translucent.

Fracture: Uneven or conchoidal, depending on the specific mineral composition and texture.

Solubility: Insoluble in common acids and alkalis, similar to quartz and opal.

Magnetism: Non-magnetic.

Fluorescence: Weak to moderate yellow or orange fluorescence under longwave ultraviolet light, often associated with the opal component.

Pleochroism: Weak, with some stones showing a slight color variation depending on viewing direction, particularly in areas with higher opal content.

Refractive Index: Varies depending on the specific mineral composition and can range from 1.45-1.55 for chalcedony and 1.40-1.45 for opal.

Read also:
Jasper - Types and varieties of Jasper (Photos)
Bumblebee Jasper - Formation, Properties, Uses, Occurrence