SAFFLORITE

Safflorite – CoAs2 – is a rare arsenide that is part of Co ores.

It is classified in the Löllingite Group, which consists of quite rare minerals. Pure safflorite practically never occurs; there is always an appreciable content of Fe and/or Ni replacing the Co, which is necessary for the stabilization of the structure. It may contain Cu, Ni, Bi, and S.

With more than 50% Fe, it forms the mineral löllingite; with more than 50% Ni, it forms the mineral rammelsbergite. There is a parallel series of antimony minerals. Safflorite is dimorphic with monoclinic clinosafflorite.

The identification of safflorite becomes easier when associated with a secondary Co mineral, erythrite, whose unmistakable wine-red color (internal reflections to NC!) is particularly conspicuous.

1. Characteristics

Crystal system: Orthorhombic bipyramidal          

Color: Tin-white, can tarnish to dark gray or it can retain its original color.     

Habit: Generally massive with a radiating fibrous structure. Granular, dendritic. Crystals are prismatic according to [010]       

Cleavage: {100} distinct.       

Tenacity: Brittle.        

Twinning: Commonly exhibits cruciform penetration twins formed by 5 individuals, which in polished section resemble stars.       

Fracture: Irregular to conchoidal.       

Mohs Hardness: 4.5 – 5.5

Parting: No.         

Streak: Grayish black.         

Lustre: Metallic.          

Diaphaneity: Opaque.           

Density (g/cm³): 6.9 – 7.3

         

2. Geology and Deposits

Safflorite forms in hydrothermal veins of medium temperature and pressure and occurs alongside other arsenic minerals as an accessory mineral in silver mining districts.

In these cases, it occurs associated with the other minerals of the paragenesis and ends up being mined for cobalt and arsenic.

Caution! Due to arsenic levels, cobalt ores must be handled with due care!

 

3. Mineral Associations

It is associated with common gangue minerals such as quartz, barite, and carbonates (calcite, dolomite, siderite).

The specific paragenesis includes a series of Co-Ni-As minerals such as arsenopyrite, skutterudite, rammelsbergite, nickeline, löllingite, linnaeite, maucherite, siegenite, parkerite, cattierite, pyrite-(Ni)(bravoite), breithauptite, and native arsenic.

Also with native silver, native antimony, native bismuth, and Ag minerals (pyrargyrite, miargyrite), Sb minerals (dyscrasite, stibarse), Bi minerals (bismuthinite), and Fe, Cu, Pb, and Zn sulfides.

As a secondary mineral, highly diagnostic(!) for Co, erythrite is formed.

 

4. Transmitted Light Microscopy

This does not apply, as safflorite is completely opaque.

5. Reflected Light Microscopy

Sample preparation: Safflorite acquires an excellent polish. Its polishing hardness is high, greater than the hardness of eskutterudite, but lower than the hardnesses of arsenopyrite, cobaltite, glaucodote and löllingite.

Samples that are heavily tarnished as hand samples can remain polished and tarnish-free for a long time in the polished sections. The properties of safflorite in the polished section, especially anisotropy, vary noticeably with variation in chemical composition.

PLANE POLARIZED LIGHT – PPL

Reflection color: White, often with a bluish tint.

Compared to the color of rammelsbergite, the color of safflorite is white, less yellow.

Compared to the color of native antimony, the color of safflorite is somewhat gray.

Compared to the color of native bismuth, the color of safflorite is bluish.

Compared to the color of native silver, the color of safflorite is grayish-white.       

Pleochroism: Very weak, ranging from yellowish to gray and bluish-white, it needs to be observed only at intergranular boundaries.

With increasing Fe content, pleochroism increases.

Reflectivity: 52.02 – 54.46%. 

Bireflectance: Minimum. 

CROSSED POLARIZED LIGHT – XPL

Isotropy / Anisotropy: Anisotropy can be very intense between dark brown and blue, especially in sections parallel to (001), but the color effects and intensity can be highly variable, making the zoning very visible.

Some grains and certain zones can be almost isotropic.

Safflorite is the mineral, among the arsenides, that shows the strongest variations in anisotropy, sometimes within the single crystal itself.

If there are strongly radioactive minerals in the vicinity of the safflorite, the anisotropy changes noticeably, and the differences in color and intensity of the different zones become smaller.

Internal reflections: No.      

May be confused with: Several other minerals in the Group, sometimes conclusive identification is impossible.

Arsenopyrite is very similar, but the grain boundaries are straighter and better defined.

Glaucodot exhibits weaker anisotropy.

Löllingite exhibits more pronounced pleochroism and stronger anisotropy.

Rammelsbergite generally shows fine lamellar twinning.

Pararammelsbergite does not show twinning.       

General Characteristics: 

Grain shape: Safflorite generally exhibits concentric or radial textures with alternating zones of safflorite with other minerals such as glaucodote, nicheline, eskutterudite, etc. It can occur in aggregates of idiomorphic crystals.

Twinning is the striking characteristic. Twins with 3 individuals (“trillings”) of helical-acicular shape according to (110) generate star-shaped sections (the “safflorite stars”), easily recognizable. Sometimes the twinned sets then intergrown in the form of a knot or form a 12-pointed star through a twin according to (101). In Crossed Nicols the twinning structure is easily recognizable.

Zoning can be very well developed.

Cleavage is not observed.

Substitutions 1: Safflorite replaces eskutterudite, rammelsbergite, native silver, galena, pitchblende, magnetite, chalcopyrite, sphalerite, niqueline, breithauptite, and cobaltite.

Substitutions 2: Safflorite is replaced by arsenopyrite, cobaltite, galena, sphalerite, marcasite, chalcopyrite, and Ag sulfosalts.

Inclusions IN safflorite can be niqueline, breithauptite, and langisite.

Inclusions OF safflorite occur in pyrite.

Intergrowths occur with native gold, arsenopyrite, and löllingite.

Safflorite 01: In PPL, calcite (dark gray), native bismuth (strong yellow) and safflorite (white/yellowish). Safflorite forms diamond-shaped crystals whose points (very typical!) are visible on the edges of the aggregate.
Safflorite 01: The same section as of the previous image, now in XPL. Calcite shows clear internal reflections, bismuth is anisotropic and safflorite shows its blue/orange anisotropy colors, VERY SIMILAR to the anisotropy colors of other arsenides!
In PPL, "star-shaped" safflorite twinning. It consists of 3 intergrown, rhomboid crystals. These twins are common when the crystals are very small.
In XPL+2º, excellent zoning is sometimes observed in the safflorite crystals, especially at the tips that stand out on the edges of the aggregates. Image obtained with high magnification objectives (40x).
In XPL, calcite (clear internal reflections) and safflorite, with its typical shapes, sometimes with zoning and twins. "Stars" formed due to twinning are not so common.
With a lot of searching and a bit of luck, you can sometimes find several "stars" formed by twins. PPL.
In this "star," it is possible to clearly distinguish the 3 crystals that form the star based on the different anisotropy colors that the crystals exhibit. XPL.
In XPL, a well-developed aggregate of safflorite, with typical shapes and anisotropy colors. With a little imagination, it is possible to recognize several "stars" formed by the twinning. In cases like this, the safflorite is easily recognizable.