The mineral collection basically consists of two main units. In the present glass cabinets standing by the walls a systematic collection can be found. In the 15 cabinets 1156 specimens of the approximately 400 exhibited mineral species can be found according to the following classification:
I. Native elements;
II. Sulphides and sulpho-salts;
III. Oxides, hydroxides;
IV. Phosphates and related compounds;
V. Sulphates and related compounds;
VI. Carbonates, borates, nitrates;
VIII. Organic minerals.
The value of the systematic collection is raised by the fact that 80% of the pieces exhibited here derive from the Carpathian-Basin. Among the native elements the grown-up gold plate, the size of which is more than 2 cm, has to be highlighted. This piece of the exhibition was found in the mines of Verespatak [today Roșia Montană, Romaina] already operating in the Roman period in the Metaliferi Mountains. The native silver represents itself both in a large pseudomorph originating from Kongsberg mines (today closed down) and in a skeletal crystal having a surprising ostrich feather form, originating from Freiberg.
From the tellurides and sulphides, the Hungarian-related nagyagite, krennerite and sylvanite pieces from the one-time goldmines of the Metaliferi Mountains are noteworthy. The small sized but wonderfully formed, shiny pieces of andorite, semseyite and fizélyite deriving from the historic Satmar mine region (Baia Mare region) also have to be highlighted.
In the shelf of the oxides, hydroxides nearly all the variants of the cryptocrystalline quartz (chalcedony, jasperite, agate) are exhibited from nearly all the classical sites (Tekerő [today: Valea Strâmbă, Romania], Kötelesmező [today: Trestia, Romania], Háromvíz [today: Garana, Romania]) within the Carpathians. The varieties of opal are represented by two splendid pieces deriving from Veresvágás [today Červenica, Slovakia] regarded to be “the Hungarian national gemstone” for centuries. The variety of forms and colours of the limonite are as rich as that of the quartz. The limonite groups deriving from the mine in Rudabánya closed down for more than a decade and the one-time Gyalár [today: Ghelari, Romania] iron mines look like abstract statues; the botryoidal and dripstone-like goethit and the goethite-druses of Gömörrákos [today: Rákoš, Slovakia] and Vashegy [Železník, Slovakia] stand out with their shiny black colour or iridescent surfaces.
Due to the good relationship of Professor Koch and his successor Gyula Grassely with Leningrad, in the 60s rather numerous specimens of minerals and rocks – deriving from the alkali rocks and their related mineralisation of the Kola Peninsula – were added to the collection. The collection was completed in a similar way with zeolites from Island, and with some attractive native sulphur, celestite and aragonite groups from the famous Sicilian sulphur mines.
However the “real treasures” of the collection are in the four cabinets standing in the middle of the hall, where the predominant majority of the specimens from the one-time private collection of Sándor Koch can be found as well. The 1058 specimen of the so called Carpathian Basin Collection covers nearly all the mine territories of the historic Hungary from a mineralogical point of view.
The systematization of the exhibited specimens is carried out in a quite unusual but still didactic way: it was carried out according to the principles of genetics. The minerals of igneous rocks and their related mineralization are followed by the minerals of the sedimentary and metamorphic geo-phases. The minerals of the present-day Hungarian deposits are presented first, and these are followed by the samples taken from the mines located in Romania and Slovakia.
The first cabinet contains wonderful specimens of secondary copper minerals originating from the oxidation-cementation zone of the Rudabánya iron metasomatic ore deposits; namely ramose native copper pieces covered with malachite, 10 cm long azurite crystals, groups of 2 cm long malachite grown up on white calcite. The malachite psudomorphosas that follows the formation of azurite crystals in the minearlization process, and the cuprite octaeder crystals that often reach 2,5 cm are the rivals of the world-famous specimens of Bisbee (Arisona), Tsumeb (Namibia) and Chessy (France) and prove that Rudabánya is unfairly not sufficiently known in the international mineralogy. Among the irreplaceable treasures of the Koch Mineral Collection skarn minerals (garnet, wollastonite, fassaite, etc.) can be also found originating from the long ago abandoned mines of the Banatian contact zone. The specimens mainly deriving from the magnetite and polimetalic contact mineralisation ofwith the granodiorite and limestone prove the great variety of the Banathian minerals. The so called “garnet series” of the collection originating from Vaskő [Ocna de Fier, Romania] and Dognácska [Dognecea, Romania] represents rhombic dodecahedron and deltoidicositetrahedron andradites of various colours mainly found in the 1910s. Such classic specimens are the hematite twins of Dognácska and the cyanotrichite from Újmoldova [Moldova Nouă, Romania] as well. The diopside groups covered with several cm long garnets, the bismuthines, the prazems and some interesting paragenesis of Vaskő (amethyste crystals on andradite and erythrite with quartz on magnetite) are worthy to be highlighted.
The second cabinet exposes the minerals mainly deriving from the once classic mine regions of Upper Hungary – today in the territory of Slovakia. The Slovak Ore Mountains are represented by wonderful siderites, by albites, tetrhedrites, sphalerites grown-up on siderites and by interestingly shaped, distorted quartz crystals deriving from the sometime Bernard mine of Rozsnyó [Rožňava, Romania]. Well-developed cinnabar and dolomite crystals, iridescent, bluish evansite from Alsósajó [Nižná Slaná, Slovakia] and various sized goethites from Dobsina can be found also.
The mines of Selmecbánya [Banská Štiavnica, Romania], the famous royal city in Upper Hungary that gave place to the Academy of Mining, are represented in the collection by well-known, imperfectly developed quartz crystals, dark violet amethyst groups, quartz minerals covered by acanthite, well-developed stephanites and sceptre quartz of unique aesthetics.
Libetbánya [Ľubietová, Slovakia], that belongs to the type of mineralization that is characteristic of the territories around Besztercebánya [Banská Bystrica, Slovakia] is a typical site of libethenite and euchroite. In the collection there are 3 beautiful mineralgroups containing well developed libethenite and the euchroite crystals, similarly to the hauerite octahedron of 2 cm size deriving from Végleskálnok [Kalinka, Slovakia].
The polymetallic mineralization of the volcanic ring of the Inner Carpathians is represented by specimens of some Hungarian sites, like Gyöngyösoroszi, Recsk, Nagybörzsöny. Besides the amethysts of Gyöngyösoroszi, the varieties of calcite and apple green fluorites deriving from the mine closed down for more than a decade are also beautiful.
A whole cabinet is occupied by minerals deriving from the Satmar mine region and representing the mineralization processes taken place in the vicinity of Nagybánya [Baia Mare, Romania]. However these mines are still operating, the Sándor Koch Mineral Collection presents a comprehensive picture about the mineral paragenesis occurring in the 50s and 60s, with special regard to the years of the world war, when these mines were temporarily reannexed to Hungary and thus the opportunity for regular collection opened up. The felsobanyite named after Felsőbánya [Baia Sprie, Romania] and the andorite groups also deriving from this site are irreplaceable. Rare silver ore, geocronites, and freieslebenite are also preserved from the dykes of the mountains of Felsőbánya that has been completely cleared off by today. Felsőbánya is far-famed for its barytes. The “series of barites” presenting the barytes of Felsőbánya is a precious part of the collection. Among the members of this series there are on the one hand some palm-sized crystals in the company of antimonite and on the other hand some surprisingly coloured baryte groups: yellows due to the orpiment inclusions, reddishes due to realgar and blacks due to boulangerite or jamesonite.
Mineralogical curiosities are the rosette-shaped pyrrhotite groups (often with vivianite) from the Salán dyke at Kisbánya [Chiuzbaia, Romania] once producing famous mineralogical miracles but today completely mined off, the pyrargyrite deriving from the mines of Kereszthegy [Dealul Crucii, Baia Mare, Romania] and the complex sulphide found and described here and named fülöppite by Sándor Koch after his friend Béla Fülöpp, a mineral collector as well. Aesthetically satisfying pleasure is provided for the visitors by the fluorites and rhodochrosite crystals of Kapnikbánya [Cavnic, Romania].
The fourth cabinet of the Carpathian Basin collection provides home for tellurides (nagyagite, krennerit, sylvanite) and for other vein-filling minerals (alabandine, rhodochrosite, realgar, quarz) of the once world-famous gold mines of the Apuseni Mountains. The precious treasure of the Sándor Koch Mineral Collection is the hessite (lead telluride) crystal that is in all probability the biggest one in the world. Though the crystal is broken, it is irreplaceable as today even the traces of the site, the once working mine of Botesbánya [Boteşti, Romania] is even hard to find.
The masterpieces of the inanimate nature could be listed for pages and pages, but the personal experience cannot be substituted this way. Professional guided tours are offered by the department for those who are interested in the particular world of the minerals. Visiting is possible all working days of the year, but it is necessary to schedule an appointment in advance.