Pohorska glažuta … Glass factories of Pohorje EarthCache

SI

Pohorska glažuta

Glažutarstvo na Pohorju

Na celotnem področju Pohorja je včasih delovalo 16 glažut ali steklarn. Zakaj toliko, ni težko ugotoviti. Vzrok je bil prisotnost kremena in neizmerno bogastvo lesa v nedotaknjenih pohorskih gozdovih. V glažutah so izdelovali »gozdno steklo«. Navadno gozdno steklo je bilo zelenkaste barve. V pohorskih steklarnah so izdelovali tudi prozorno, razbarvano ter barvno steklo (rumenkasto, rjavkasto in modro). Med izdelki zasledimo kozarce, kozarce na nogi, kelihe, lekarniško steklo, embalažno steklo, vrtne krogle, svečnike, ...

Pohorsko steklo

Pohorje je del vzhodnih Alp in je edino silkatno gorovje v Slovenij. Geološka zgradba Pohorja je izjemno pestra. Je največji masiv magmatskih in metamorfnih (preobraženih) kamnin v Sloveniji. Jedro Pohorja, ovršni del z vrhovi in oblimi pobočji, sestavljajo magmatske kamnine, katerih starost je 18 milijonov let. Najbolj znana magmatska kamnina je granodiorit (staro ime zanjo je granit, tonalit). Okrog jedra so razporejene metamorfne (preobražene) kamnine, ki so stare več kot 400 milijonov let. Nastale so s preobrazbo sedimentnih in magmatskih kamnin in so najstarejše slovenske kamnine. Najbolj znane so gnajs, blestnik, eklogit.

Granodiorit
Je metamorfna kamnina sive barve, prepredena z belimi apelitnimi žilami. Je intruzivna magmatska kamnina (globočnina) podobna granitu, vendar vsebuje več plagioklaza kot ortoklaza. Uradno je definiran kot faneritska magmatska kamnina z več kot 20 volumskimi odstotki kremena (SiO2), v glinencih pa je najmanj 65% plagioklaza. Običajno vsebuje veliko biotitne sljude in amfibola in je zato temnejši od granita. Sljuda ima lahko dobro formirane heksagonalne, amfibol pa igličaste kristale.
Granodiorit je relativno lahka kamnina z gostoto od 2,64 do 2,70 g/cm3. Praviloma je grobo ali srednje zrnata kamnina od sive do belo sive barve. V granodioritih porfiritskega tipa z neenakomerno velikostjo zrn lahko kristali glinenca dosežejo velikost do nekaj centimetrov. Smeri zrn mineralov so navidezno neurejene, podrobnejše preiskave pa vendarle pogosto pokažejo urejeno teksturo glinencev. Za kamnine magmatskega izvora takšna tekstura ni nič nenavadnega.
Med spremljajočimi minerali so najpogostejši alanit, apatit, titanit in cirkon, včasih tudi epidot in cojzit. Granodiorit je kot neprozoren rudni mineral pogosto podoben ilmenitu in magnetitu. Granodioriti z manj kot 5% temnih mineralov, predvsem biotita in rogovače, so levko-granodioriti, tisti z več kot 25% pa mela-grandioriti.

Granodioriti imajo najpogosteje naslednjo sestavo (v volumskih odstotkih):
kremen: 19 do 26 %
alkalni glinenec: 17 do 21 %
plagioklaz: 44 do 48 %
biotit: 3 do 10 %
rogovača: 0 do 7%
klinopiroksen: prisoten v izjemnih primerih
spremljajoči minerali in rudnine: do 1,5 %

V Sloveniji se kremenov granodiorit nahaja v osrednjem delu Pohorja, kjer je v terciarju prodrl na površje kot lakolit (čok) in je najstarejša metamorfna kamnina na našem ozemlju. Kamnino so včasih imenovali tonalit, vendar so ime spremenili, ker ni ustrezalo njegovi mineraloški zgradbi. Najbolj znana skulptura iz granodiorita je Kamen iz Rosette.

Gnajs

Gnajs je pogost in splošno razširjen tip kamnine, nastale v visoko kvalitetnih regionalnih metamorfnih procesih že obstoječih formacij, ki so bile prvotno bodisi magmatske ali sedimentne kamnine. Je zrnata skrilava metamorfna kamnina z alkalnimi glinenci, kremenom in sljudo kot bistvenimi minerali. Pogosto je listasta (foliacija – plastnata tekstura metamorfnih kamnin, ki vsebujejo listaste silikate). V foliaciji so značilni izmenično temnejši in svetlejši barvni pasovi, ki se imenujejo "gnajsovi pasovi".

Zanimiva je sestava. Gnajsove kamnine so običajno srednje do grobo listaste; so v veliki meri rekristalizirane, vendar ne vsebujejo velike količine sljude, klorita ali drugih mineralov. Gnajsi, ki so se preobrazili iz magmatskih kamnin ali njihovega ekvivalenta, se imenujejo granitni gnajsi, dioritni gnajsi itd. Gnajsove kamnine se lahko poimenujejo po značilnih komponentah, kot so granatni gnajs, biotitov gnajs, albitni gnajs itd. Ortognajs označuje gnajs, izpeljan iz magmatskih kamnin, paragnajs je iz sedimentnih kamnin.

Gnajsovi pasovi se pojavljajo v črtastih pasovih. Razvili so se pod visokimi temperaturnimi in tlačnimi pogoji. Minerali so razporejeni v plasteh, ki se pojavljajo kot pasovi v prerezu. Temnejši pasovi imajo relativno bolj mafične minerale (tiste, ki vsebujejo več magnezija in železa). Svetlejši trakovi vsebujejo relativno večjo felzičnost (silikatne minerale, ki vsebujejo več lažjih elementov, kot so silicij, kisik, aluminij, natrij in kalij). Pogost vzrok pasov je izpostavljanje protolita (prvotni material, ki je bil podvržen metamorfizmu) skrajni strižni sili, drsni sili podobni potiskanju proti vrhu v eno smer in dna v drugo smer. Te sile raztegnejo skalo podobno plastiki in osnovni material se razprostre v listih. Nekateri pasovi se tvorijo iz prvotnega kamnitega materiala (protolita), na katerem je skrajna temperatura in tlak, ki je sestavljen iz izmeničnih plasti peščenjaka (svetlo) in skrilavca (temnejše), ki se je preoblikoval v pasove kremena in sljude. Drug vzrok za pasove je metamorfna diferenciacija, ki ločuje različne materiale v različne plasti s pomočjo kemijskih reakcij, proces ni v celoti razumljen.

Lastnosti gnajsa:

• Mineralna sestava: Gnajs je sestavljen iz različnih mineralov, vključno z žarčevino, kvarcem, plagioklasom, ortoklasom, biotitom, in drugimi.
• Zrnatost in tekstura: Gnajs ima zrnato teksturo, kjer so mineralna zrna jasno vidna. Zrnata tekstura se razlikuje glede na vrsto mineralov in stopnjo metamorfizma.
• Usmerjenost mineralov: Zaradi procesa metamorfizma se minerali v gnajsu lahko porazdelijo v določeni usmeritvi, kar daje kamnini foliacijo (plastnatost).
• Bleščeči vzorci: Zaradi izrazitih mineralov, kot je žarčevina, mnogi gnajsi izražajo bleščeče vzorce, ki jih lahko vidimo s prostim očesom.
• Barva: Barva gnajsa je odvisna od prisotnosti mineralov. Lahko je siv, roza, rdeč, črn, zelen ali drugih odtenkov.
• Trdnost: Gnajs je splošno znan po svoji trdoti in vzdržljivosti. To ga naredi za priljubljen gradbeni material in kamnino v umetniških aplikacijah.
• Sestava plasti: Plasti v gnajsu so pogosto razločne in se imenujejo gnajsne linije. Te linije so posledica strukturalnih in mineralnih razlik med plastmi.
• Stratigrafske značilnosti: Gnajs se lahko pojavi v povezavi z drugimi metamorfnimi kamninami ali tvori posebno stratigrafsko enoto.
• Uporaba: Gnajs ima gospodarske uporabe v gradbeništvu, kot okrasni kamen in kot surovina za proizvodnjo drugih materialov.

Blestnik

Blestnik je skrilava metamorfna kamnina. Kamnina nastane pri usmerjenih tlakih, zaradi česar se razvije skrilava tekstura. Največkrat nastane s spremembo oz. metamorfozo drobnozrnatih sedimentnih kamnin, kot je muljevec. Temperatura in tlaki nastanka blestnika so višji kot pri nastajanju filita in nižji kot pri gnajsu. Kamnina je sestavljena iz mineralnih zrn, pri katerem so nekatera velika do nekaj mm in jih zato vidimo s prostim očesom. Je zanimiva na pogled, saj se zaradi lepo vidnih sljudnih mineralov blešči. Posebej zanimiv je mineral muskovit, ki daje kamnini videz, kot da so po njej razporejena mala bleščeča ogledalca.

Značilnosti blestnika imenovanega tudi sljudni skrilavec:

• Sestava: Blestnik je običajno sestavljen iz mikroskopskih lističev minerala glinice (glina) in mika. Ti minerali so posledica metamorfnih procesov.
• Struktura: Zaradi usmerjenosti mineralov v določeni smeri blestnik pogosto kaže foliacijo, kar pomeni, da se lahko loči v tanke plasti ali lističe.
• Barva: Barva blestnika se lahko razlikuje, vendar je pogosto siva, zelena, rjava ali črna, odvisno od mineralne sestave in drugih dejavnikov.
• Fleksibilnost: Blestnik je lahko zelo fleksibilen in se lahko razcepi v tanke, prožne lističe. Ta lastnost je pogosto izkoriščena pri proizvodnji škrilavčastih plošč ali ploščic.
• Starost: odvisna je od različnih dejavnikov, vključno s starostjo izvorne kamnine, pogoji metamorfizma in geološko zgodovino območja. Blestnik se tvori skozi proces metamorfizma, ki vključuje visoke temperature in pritisk, kar lahko traja milijone let.
• Geološko obdobje: Blestnik se lahko oblikuje v različnih geoloških obdobjih, vendar se pogosto povezuje z regionalnim ali kontinentalnim metamorfizmom, ki je lahko povezan z gorskimi oblikovanji ali drugimi tektonskimi dogodki. Natančna starost posameznega blestnika bo odvisna od geoloških razmer in značilnosti določenega območja, zato je težko podati natančen časovni okvir brez specifičnih informacij o lokaciji
• Uporaba: Zaradi svoje fleksibilnosti in odpornosti proti razcepu je blestnik pogosto uporabljen za izdelavo strešnikov, ploščic, škarnikov in drugih gradbenih materialov. Uporablja se tudi v umetnosti in obrti ter kot dekorativni kamen.

Kremen
Kremen, tudi kremenjak ali kremenica, je trda sedimentna kriptokristalinska kamnina steklastega videza. Kremen je kristal silicijevega dioksida (SiO2). V naravi ga dobimo v obliki kremenčevega peska, ki je navadno sive, črne, modre ali temno rjave barve, ki lahko vsebuje celo do 99,7 SiO2. V glavnem se pojavlja v grudah in gmotah v kredi in apnencu. Ima zelo dobro mehansko trdnost, kemično obstojnost ter optične in piezoelektrične lastnosti. Ima trdoto 7 na Mohsovi trdotni lestvici. Dobro prevaja toploto, zato  v stiku s kožo deluje hladno. Pri normalnih pogojih se le malo topi v vodi. Ob povišanem pH se ga raztopi več. Pri znižanju tlaka in temperature se raztopine prenasičijo in pride do  kristalizacije. Pogoji, pri katerih raste, vplivajo na zunanji izgled. Če je prostora dovolj, nastanejo lepi kristali. Vendar se v nekaj milijonih let v naravi kremenovim kristalom marsikaj zgodi. Zaradi zmrzali in vročine kristal poči, erozija ga odnese in zdrobi, pretvori se nazaj v drobna zrna, ki jih odplavi do morja, kjer se usedejo na dno in pretvorijo v sedimentno kamnino.

Kremenčevo steklo: Če se talina silicijevega dioskida ohladi dovolj hitro, ne kristalizira, ampak se strdi kot steklo. Temperatura steklastega prehoda čistega SiO2 je okrog 1600 K (1330 °C). Lokalna atomska zgradba čistega kremenčevega stekla je enaka kot v večini drugih kristaliničnih polimorfov in ima obliko tetraedra. Razlika med steklom in kristali je v povezavi teh tetraedrskih enot. V kremenčevem steklu tetraedri ne tvorijo ponovljive mreže, vsi kisikovi atomi pa povezujejo samo po dva sosednja tetraedra. Čeprav struktura stekla na večjih razdaljah ni ponovljiva, je kljub temu značilno urejena na razdaljah, ki daleč presegajo dolžino vezi. Primer takšne ureditve je tvorjenje obročev, sestavljenih iz šestih tetraedrov [SiO4].

Čisti in popolni kremenovi kristali se imenujejo kamena strela (tudi kvarc). Taki kristali so prozorni in brezbarvni. Že ob majhnih količinah različnih primesi se kremenovi kristali obarvajo in lahko postanejo motni. Kremen je eden najbolj razširjenih mineralov v zemeljski skorji, saj zavzema kar 12 odstotkov njene prostornine.

Recepti steklarja Avguština Zinkeja na Gornji glažuti za pripravljanje stekla in barv

V receptih za steklo vidimo, da je glavna sestavina pesek. To je kremenčev pesek, ki so ga dobili z drobljenjem kremena ali kisa SiO2 . Vzhodni del Črnega vrha, ob poti, ki nas vodi od Pastirskega stola do Ribniške koče, domačini še danes imenujejo Kis jama. Na terenu se vidi, da je bilo od tam odstranjenega zelo veliko materiala. Kremen je tudi sicer na Pohorju zelo razširjena kamnina.
Kaj je pepelika? To je neke vrste lug, ki so ga pridobivali iz pepela. Veliko pepela, ki so ga pridobivali iz najmanj kvalitetnega lesa so dali v velike kotle in kuhali. Potem so odlili lužno tekočino in jo ponovno kuhali, tako da je izhlapela vsa voda, na dnu je ostala pepelika, približno 2 kg iz enega kubičnega metra lesa.

Vprašanja:

1. Stojiš na točki, kjer so včasih kopali rudo za izdelavo stekla. Katero izmed štirih zgoraj opisanih kamnin najdeš na lokaciji.
2. V okolici poišči dva kamna in ju podrgni med seboj. Kaj opaziš, predvsem če je zunaj tema?
3. Ko si dva kamna podrgnil med seboj, ju povohaj. Ali kaj vohaš ali ne?
4. Ob manjši navpični skali pri klopcah naredite fotografijo sebe ali vašega osebnega predmeta in jo objavite v logu. Fotografija mora vsebovati vaše GC ime in datum obiska, napisano na papirju ali kjerkolipačže. Fotografija je obvezna (enako kot pri virtualnih zakladih).

Preden vpišete obisk Geološkega zaklada, pošljite odgovore na elektronski naslov nisem.geocacher@gmail.com ali preko GC profila. Takoj potem lahko vpišete obisk Geološkega zaklada na spletu, za kar ne potrebujete dodatnega dovoljenja. V primeru napačnih odgovorov vas bom kontaktiral.

Dan zemeljskih zakladov

Vsako drugo soboto in nedeljo v oktobru je dan zemeljskih zakladov. Najdba v teh 2 dneh vam vsako leto prinese nov spominek v vaš profil. Ta vikend je ponavadi odprt dostop do vseh zemeljskih zakladkov, tudi tistih, ki so premium.

Drugi vikend v oktobru je dan zemeljskih zakladkov

Viri:

EN

Glass factories of Pohorje

Glass factories of Pohorje

There used to be 16 glass factories (slo: glažuta) on the Pohorje region. The reason for this abundance is not hard to determine. The presence of quartz and immense wealth of wood in the untouched Pohorje forests played a significant role. These glass factories produced "forest glass." Typically, forest glass had a greenish color. In the Pohorje glassworks, they also crafted clear, decolored, and colored glass (yellowish, brownish and blue). The glass products were glasses, stemmed glasses, goblets, pharmacy glass, packaging glass, garden globes, candleholders and more.

Pohorje glass

Pohorje is part of the Eastern Alps and is the only silicate mountain range in Slovenia. The geological structure of Pohorje is exceptionally diverse. It is the largest massif of igneous and metamorphic (transformed) rocks in Slovenia. The core of Pohorje, the summit part with peaks and gentle slopes, is composed of igneous rocks with an age of 18 million years. The most well-known igneous rock is granodiorite (formerly known as granite, tonalite). Surrounding the core are arranged metamorphic rocks, which are more than 400 million years old. They originated through the transformation of sedimentary and igneous rocks and are the oldest rocks in Slovenia. The most famous ones include gneiss, mica schist, and eclogite.

Granodiorite
It is a metamorphic rock of gray color, interlaced with white aplite veins. It is an intrusive igneous rock (plutonic), similar to granite but containing more plagioclase than orthoclase. Officially defined as a phaneritic igneous rock with over 20% volumetric silica (SiO2), with at least 65% plagioclase in feldspar. Typically, it contains a significant amount of biotite mica and amphibole, making it darker than granite. Mica can have well-formed hexagonal crystals, while amphibole can have needle-like crystals.
Granodiorite is a relatively light rock with a density ranging from 2.64 to 2.70 g/cm3. Generally, it is a coarse to medium-grained rock ranging from gray to white-gray. In porphyritic granodiorites with uneven grain sizes, feldspar crystals can reach sizes of several centimeters. The mineral grain orientations may appear disordered, but detailed examinations often reveal an ordered texture of feldspar. For magmatic rocks, such texture is not uncommon.
Among the associated minerals, the most common are allanite, apatite, titanite, and zircon, sometimes including epidote and coesite. Granodiorite, as an opaque ore mineral, can often resemble ilmenite and magnetite. Granodiorites with less than 5% dark minerals, primarily biotite and hornblende, are leuco-granodiorites, while those with more than 25% are melanogranodiorites.

Granodiorites most commonly have the following composition (in volumetric percentages):
quartz: 19 to 26%
alkali feldspar: 17 to 21%
plagioclase: 44 to 48%
biotite: 3 to 10%
hornblende: 0 to 7%
clinopyroxene: present in exceptional cases
associated minerals and ores: up to 1.5%

In Slovenia, quartz granodiorite is found in the central part of Pohorje, where it intruded to the surface as a laccolith (plug) in the Tertiary period and is the oldest metamorphic rock in our territory. The rock was formerly called tonalite, but the name was changed because it did not match its mineral composition. The most famous sculpture made of granodiorite is the Rosetta Stone.

Gneiss

Gneiss is a common and widely distributed type of rock formed in high-quality regional metamorphic processes of pre-existing formations, which were originally either igneous or sedimentary rocks. It is a granular schistose metamorphic rock with alkali feldspar, quartz, and mica as essential minerals. It often exhibits foliation (layered texture of metamorphic rocks containing platy silicates). In foliation, alternating darker and lighter-colored bands, called "gneissic bands," are characteristic.

Its composition is intriguing. Gneissic rocks are typically moderately to coarsely foliated; they are highly recrystallized but do not contain a large amount of mica, chlorite, or other minerals. Gneisses transformed from igneous rocks or their equivalents are called granitic gneisses, dioritic gneisses, etc. Gneissic rocks can be named after characteristic components, such as garnet gneiss, biotite gneiss, albite gneiss, etc. Orthogneiss denotes gneiss derived from igneous rocks, while paragneiss comes from sedimentary rocks.

Gneissic bands occur in streaks. They developed under high-temperature and pressure conditions. Minerals are arranged in layers, appearing as bands in cross-section. Darker bands contain relatively more mafic minerals (those containing more magnesium and iron). Lighter bands contain relatively more felsic minerals (silicate minerals containing more light elements like silicon, oxygen, aluminum, sodium, and potassium). A common cause of banding is the exposure of protolith (original material subjected to metamorphism) to extreme shearing forces, thrust-like sliding forces towards the top in one direction and the bottom in the other. These forces stretch the rock like plastic, and the original material spreads into layers. Some bands are formed from the original rock material (protolith) where extreme temperature and pressure created alternating layers of sandstone (light) and shale (darker), which transformed into bands of quartz and mica. Another cause of bands is metamorphic differentiation, separating different materials into different layers through chemical reactions, a process not fully understood.

Characteristics of gneiss:

• Mineral composition: Gneiss is composed of various minerals, including feldspar, quartz, plagioclase, orthoclase, biotite, and others.
• Grain size and texture: Gneiss has a granular texture where mineral grains are clearly visible. Grain size texture varies based on the type of minerals and the degree of metamorphism.
• Mineral alignment: Due to the metamorphic process, minerals in gneiss can be aligned, giving the rock foliation (layering).
• Shiny patterns: Due to distinct minerals like feldspar, many gneisses exhibit shiny patterns visible to the naked eye.
• Color: The color of gneiss depends on the presence of minerals. It can be gray, pink, red, black, green, or other shades.
• Hardness: Gneiss is known for its hardness and durability, making it a popular construction material and a rock in artistic applications.
• Layer composition: Layers in gneiss are often distinct and called gneissic lines. These lines result from structural and mineral differences between the layers.
• Stratigraphic features: Gneiss may appear in association with other metamorphic rocks or form a distinct stratigraphic unit.
• Usage: Gneiss has economic uses in construction, as decorative stone, and as a raw material for the production of other materials.

Mica (blestnik)

Mica schist is a schistose metamorphic rock. The rock forms under directed pressures, resulting in a schistose texture. It most commonly develops through the alteration or metamorphism of fine-grained sedimentary rocks such as shale. The temperatures and pressures involved in the formation of mica schist are higher than those for phyllite but lower than those for gneiss. The rock is composed of mineral grains, some of which are large, up to a few mm, making them visible to the naked eye. It is visually interesting as it sparkles due to the prominently visible mica minerals. Particularly fascinating is the mineral muscovite, giving the rock the appearance of being adorned with small glittering mirrors.

Characteristics of mica schist, also known as schistose slate:

• Composition: Mica schist is typically composed of microscopic flakes of minerals such as clay and mica. These minerals result from metamorphic processes.
• Structure: Due to the alignment of minerals in a specific direction, mica schist often exhibits foliation, meaning it can be separated into thin layers or sheets.
• Color: The color of mica schist can vary but is often gray, green, brown, or black, depending on the mineral composition and other factors.
• Flexibility: Mica schist can be very flexible and can split into thin, flexible flakes. This property is often utilized in the production of slate-like sheets or tiles.
• Age: It depends on various factors, including the age of the original rock, metamorphic conditions, and the geological history of the area. Mica schist forms through the process of metamorphism, involving high temperatures and pressure, which can span millions of years.
• Geological Period: Mica schist can form in different geological periods but is often associated with regional or continental metamorphism linked to mountain-building events or other tectonic activities. The precise age of a specific mica schist will depend on the geological conditions and characteristics of a particular area, making it challenging to provide an accurate timeframe without specific location details.
• Usage: Due to its flexibility and resistance to splitting, mica schist is commonly used in the production of roofing, tiles, flagstones, and other construction materials. It is also employed in art and crafts and as a decorative stone.

Quartz

Quartz, also known as chert or flint, is a hard sedimentary cryptocrystalline rock with a glassy appearance. Quartz is a crystal of silicon dioxide (SiO2). In nature, it is found in the form of quartz sand, typically gray, black, blue, or dark brown, and can contain up to 99.7% SiO2. It mainly occurs in nodules and masses in chalk and limestone. Quartz exhibits excellent mechanical strength, chemical stability, as well as optical and piezoelectric properties. It has a hardness of 7 on the Mohs scale. It conducts heat well, giving a cool feeling when in contact with the skin. Under normal conditions, it is only slightly soluble in water, but its solubility increases with elevated pH. Lowering pressure and temperature can lead to supersaturation of solutions and crystallization. The conditions under which it grows influence its external appearance. If there is enough space, beautiful crystals can form. However, over millions of years in nature, quartz crystals undergo various changes. Due to frost and heat, crystals may crack, erosion carries them away and crushes them, transforming them back into tiny grains that are washed to the sea, where they settle on the seabed and turn into sedimentary rock.

Quartz Glass: If the melt of silicon dioxide cools rapidly enough, it does not crystallize but solidifies into glass. The temperature of the vitreous transition of pure SiO2 is around 1600 K (1330 °C). The local atomic structure of pure quartz glass is the same as in most other crystalline polymorphs and takes the form of tetrahedra. The difference between glass and crystals lies in the connection of these tetrahedral units. In quartz glass, tetrahedra do not form a repeatable network, and all oxygen atoms connect only two adjacent tetrahedra. Although the glass structure is not repeatable at larger distances, it is still characteristic and organized at distances far exceeding the bond length. An example of such organization is the formation of rings composed of six tetrahedra [SiO4].

Pure and flawless quartz crystals are called rock crystal (also quartz). Such crystals are transparent and colorless. Even in small amounts of various impurities, quartz crystals can become colored and cloudy. Quartz is one of the most widespread minerals in the Earth's crust, constituting as much as 12% of its volume.

Glassmaker Avguštin Zinke's Recipes at Gornja Glažuta for Glass and Colors Preparation

In glass recipes, we see that the main ingredient is sand. This is quartz sand obtained by crushing quartz or silica SiO2. The eastern part of Črni Vrh, along the path leading from Pastirski Stol to Ribniška Koča, is still called Silica cave(Kis Jama) by the locals. In the field, it is evident that a significant amount of material was removed from there. Quartz is also a very common rock on Pohorje.

What is "potash (prepelika)"? It is a kind of lye obtained from ash. They put a lot of ash, obtained from the least quality wood, into large cauldrons and boiled it. Then they poured off the lye liquid and boiled it again, evaporating all the water. At the bottom, "potash" remained, approximately 2 kg from one cubic meter of wood.

Questions:

Please send the answers to nisem.geocacher@gmail.com or via your GC profile before signing up for an Earth cache. You can write a find log online immediately afterwards without my reply. In case of incorrect answers I will contact you.

Earthcache day

Every second saturday and sunday in October is Earthcache day. Finding a cache in these 2 days brings you a new souvenir in your profile every year. This weekend is usually open access to all Earthcaches including premium.

Second weekend in October is Earthcache day