Mineralogical-Petrographical Investigation and Usability as the Gemstone of the North Anatolian Kammererite, Tokat, Turkey

Abstract

Kammererite formations were observed in the region of Tokat province in the north of Anatolia. Kemmererite (purple, reddish, pink color) is present in the form of nodules or veins in chromium levels found in Mesozoic basic-ultrabasic rocks. In the surveys, it was found that archerite minerals do not show a widespread distribution and have different shades of pink and color and glassy brightness. Thin-section analyses were performed from kammererite samples. In the investigations, kammererite mineral showed brownish or pinkish pleochroism in plane-polarized light. In crossed polars, it was observed that they had interference color in grayish tones. Due to its low hardness, kammererite was treated with epoxy to increase its durability. In addition, it has been determined that they can be used in both jewelry and ornamental objects with the applied cabochon cutting styles.

1. Introduction

Kammererite mineral, which is rarely found in the world, is found in chromite deposits as reddish pink or purple-violet [1] colors as transparent or semitransparent. Its hardness is around 2.5, and its specific weight is 2.645 g/cm³ [2, 3].

Kammererite mineral is one of the clinochlorine members of chlorite group in phyllosilicates. Clinochlore, which is one of the most common members of the chlorite group minerals [4], can be divided into three subvarieties according to body colors and implicational abundance of the main cations [5, 6, 7, 8, 9, 10, 11]. These are blackish-green or bluish-green colored clinochlore (ferroan clinochlore) [12], yellowish-green or green colored clinochlore (magnesian clinochlore) [13, 14], and magenta colored clinochlore (chromian clinochlore) [5, 11, 15, 16, 17]. In fact, it is well-known that the name clinochlore derived from “clino,” which refers to the inclined optical axes and the Greek “chloros,” for “green,” its most typical color [4, 11, 18, 19].

Chromian clinochlore (kammererite) represented by the formula [Mg₅(Al,Cr,Fe)₂Si₃O₁₀(OH)₈] [8, 9] is a hydrous silicate with a monoclinic IIb-2 polytype, with symmetry C² = m, and is extremely rare and of high interest for mineral collectors [20].

Worldwide occurrences of chromian clinochlore (kammererite) in addition to Turkey are as follows: Australia (Coobina chromite mine, Sylvania Station, Meekatharra Shire, Western Australia), Austria (Gulsen, Sommergraben, Lobminggraben, Leoben, Styria), Ethiopia (Tumut River, Sosua Region, Benishangul-Gumaz Province), Finland (Elijarvi Cr Mine, Kemi, Lapland Region), Greece (Nea Roda, Chalkidiki Prefecture Macedonia), Italy (Locana, Orco Valley, Torino Province, Piedmont), Japan (Akaishi Mine, Ehime Prefecture, Shikoku Island), Russia (Poldnevaya village, Sverdlovsk Oblast, Middle Urals), and the United States, (Dunsmuir, Siskiyou Co., California; Cecil Co., Maryland; Green Mountain Mine, Day Book, Yancey Co., NC; Jackson Co., Oregion; Woods Chrome Mine, Texas, Little Britain Township, Lancaster Co., PA) [20].

2. Material and methods

Samples were taken from the study area in order to determine the distribution, the paragenetic relationships, and the mineralogical, geochemical, and gemological characteristics of kammererite. It has been engraved on 1/25000 map. Thin sections were prepared from kammererite and side rock samples taken from the field in thin-section laboratory of Kırşehir Ahi Evran University Geological Engineering Department. Mineralogical determinations (mineral paragenesis) were carried out by examining these samples under a polarizing microscope in Kırşehir Ahi Evran University Geological Engineering Mineralogy-Petrography Laboratory.

In addition, gem-cutting techniques were applied to the kammererite samples taken from the field by using diamond coating saw, sinter diamond abrasive discs and polishing machine, and the usability of kammererites as a gemstone was present.

Kammererite samples taken from the study area applied gem-cutting techniques in the Gemology Laboratory of Mersin University, School of Jewelry Technology and Design.

First, slices of coarse material were taken on the large cutting machine, and different shapes were marked. Edge trimming was done on the small cutting machine, and curves were made on the cabochon machine. Finally, abrasive and polishing processes were carried out to form cabochon stones. Because kammererite are fine grains and fine veins, it cannot be processed alone. For this reason, it was worked together with the side rock. The obtained gems can be used in jewelry as necklaces, rings, earrings, bracelets, brooches, and functional goods such as keychains.

Treatment studies of kammererite samples were carried out in the natural stone analysis laboratory of Kaman Vocational School of Kırşehir Ahi Evran University. First, the samples were kept in the oven at 75°C for one day to allow them to completely exhale. Then, the hot samples were kept in the mixture of epoxy and hardener for 1 day. As a result, the epoxy penetrated the capillary cavities of the samples, and the samples had a solid structure. Epoxy-treated specimens were processed using cabochon and simple step cutting methods.

3. Geology

The study area is located in the Middle Pontid Tectonic Belt [21], south of Tokat province.

Tokat metamorphites [22], which represent the oldest unit in the study area and contain schist, phyllite, marble, and metabasites, are Upper Paleozoic-Triassic and are overlain by Mesozoic basic and ultrabasic rocks which are part of the ophiolitic series (Figure 1). These basic and ultrabasic rocks are overlain by Upper Cretaceous volcanic and sedimentary units. The youngest units in the study area are Quaternary alluviums.

Figure 1.

Geological map of the study area [23].

4. Findings

4.1 Field studies

Kammererite formations in the region including Beşören and Saltık Villages within the borders of Tokat province in northern Anatolia are in purple-violet and reddish pink color and are in the form of nodules (Figure 2a,b,d,e) or veins (Figure 2c,f) within the chromium levels within the Mesozoic basic-ultrabasic rocks reaching up to 40 cm (Figure 3).

Figure 2.

View of kammererites in the field (kammererite nodules—a, b, d, and e; kammererite veins—c and f).

Figure 3.

Close-up view of kammererite samples taken from the study area.

4.2 Mineralogical-petrographical-gemological investigations

Thin sections prepared in order to determine the mineral associations and textural relationships of the rock samples taken from the study area were examined under a polarizing microscope. Chromium minerals are observed as black color in plane-polarized light and crossed polars because they are opaque minerals (Figure 4).

Figure 4.

Combination of chromium (Chr) and kammererite (Kae) minerals (a, c, e, g—crossed polars; b, d, f, h—plane-polarized light).

Kammererite minerals has microcrystalline size. While the colorless, grayish, brownish, and pinkish pleochroism was observed in the plane-polarized light in the kammererite mineral (Figure 4b,d,f,h), the interference colors in black and white gray tones were observed in the crossed polars (Figure 4a,c,e,g).

It was observed in the surface investigations that kammererite minerals did not show a widespread distribution. Kammererite minerals in the study area have different shades of pink color and glassy brightness and are either transparent or semitransparent.

First, kammererites were processed without any treatment (Figure 5a). They have low durability and very fine grain mineral composition. For this reason, treatment has been made in kammererite. Gemmologically better products were obtained (Figure 5b).

Figure 5.

Gemstones made from kammererite samples taken from the study area (a—processed samples without treatment; b—processed samples after treated with epoxy).

5. Results

Kammererites in the study area are in the form of nodules or thin veins at chromium levels within the basic-ultrabasic rocks of the Mesozoic age. As a result of the surface study carried out in the study area, it is observed that the kammererites formation does not show much spread. They are found in different shades of pink in the field with abundant cracked cracks. Thin sections made from kammererite samples taken from the field are colorless, grayish brownish, and pinkish pleochroism in plane-polarized light. In crossed polars, interference colors are observed in black and white gray tones. The opaque minerals that are impermeable to light are the chromium minerals.

Bir mineralin süstaşı olarak kullanılabilmesi için temel özelliklerden olan, nadir bulunma, dayanıklılık, güzellik (renk, saydamlık vb.), işlenebilirlik özelliklerini barındırması beklenmektedir. Inceleme alanındaki Kemereritler nadir bulunma, güzellik ve işlenebilirlik özelliklerine sahiptir. Düşük dayanıklılığı ise iyileştirme yöntemleri ile arttırılabilir. Rarity, durability, beauty (color, transparency, etc.), and processability which are the basic properties of gemstones are expected from a mineral for being used as gemstones. Kammererites in the study area have rarity, beauty, and processability properties. Its low durability can be increased by treatment methods.

As a result of the lapidary studies made from the samples taken from the study area, it was observed that kammererite minerals can be processed together with the side rock and used in jewelry and ornamental production. However, the low hardness of kammererites, while facilitating workability, adversely affects their durability. For this reason, after the treatment (with epoxidation method), both increased durability and visually appealed.

Considering the rarity of studies related to the rarity of kammererite in the world, this study is also important in terms of providing resources for those working and researching in this field.

Acknowledgments

This study was carried out within the scope of the project of MMF.A4.18.014 supported by Kırşehir Ahi Evran University Scientific Research Projects Coordination Unit. We would like to extend our thanks to the Kırşehir Ahi Evran University Scientific Research Projects Coordination Unit, which provided financial support to carry out this work.

Conflict of interest

The authors declare no conflict of interest.