Larvikit er en grovkornet magmabjergart, hvis hovedbestanddel er labradoriserende korn af alkalifeldspat. Den opbygger et stort område omkring Larvik i den geologiske provins Oslofeltet og findes i Danmark som ledeblokke eller vandresten. Næsten 90 procent af larvikitten består af feldspar, og krystallerne er sammensat således, at et blåt farvespil vises, når lyset bryder ind i små lameller internt i dem. Vi kalder dette optiske fænomen for iridescens- eller Schiller-effekten. Det er den meget specielle sammensætning af feltet spat, hvilket er årsagen til dette. Foruden feldspar indeholder larvikit små mængder af mørke mineraler, såsom amfibol, olivin og biotit, og de mest attraktive sorter bærer små mængder af mineralske nepheliner. Larveroverfladen er klassificeret som monzonit i et QAP diagram, se nedenfor. En monzonit har omtrent lige store mængder plagioclase og alkali feldspar og mindre end 5% kvarts (lys hvidglimmer). Larvikit anvendes pga. det smukke farvespil som facadesten og har vundet vid udbredelse. Bjergarten er en varietet af augitsyenit/monzonit, som er en vigtig bjergart i mange magmaprovinser, som blandt andet kan ses i sydgrønland.

 

Vandreblok

En vandreblok (også kaldet en erratisk blok; fra latin erratus: på afveje, dvs. geologisk fejlplaceret) er en (ofte meget stor) sten af en bjergartstype, der kun findes som faststående fjeld langt fra stenens placering, ofte flere hundrede km. Vandreblokke er blevet ført med af indlandsisen (under istiden) og efterladt da isen smeltet (det der ofte, noget fejlagtigt, benævnes "da den trak sig tilbage"). Hvis stenens oprindelse kan stedfæstes, kan den afsløre, hvilke egne isen har passeret undervejs.

Danmarks største vandreblok er Hesselagerstenen i nærheden af Nyborg på Fyn.

Her er GC koden til earthcachen 

Opgave: 

1. Studér og observer de særlige kendetegn ved Larvikit på stenen ved hjælp af en lommelygte. Hvad sker der?

1.1 Undersøg størrelsen af larvikitets krystalkorn og hvor store vil du vurdere dem til at være?

2. På koordinaterne kan du se, at der er revner i stenen, da en ukendt landmand i 1920'erne, forsøgte at sprænge stenen i stykker. hvor mange "små sten" kan du tælle her ?

3. Tag gerne et billede af dig selv, eller din GPS, på stenen. Dette er ikke et krav for logningen.

Send din opdagelse og en forklaring til min profil-mail (Team Hvisthule)

Send venligst først svarene som retningslinjerne siger, ellers vil jeg slette din log uden kommentar. Jeg kommer i kontakt, hvis det er nødvendigt. Med svarene skal der være tvetydigheder.

Kilde angivelse: Oplysningerne til cachen stammer hovedsaligt fra VisitHerning, Wikipedia samt Henning Sørensen: larvikit i Den Store Danske, Gyldendal. Hentet 17. marts 2019 fra http://denstoredanske.dk/index.php?sideId=114785

 

 

Mørupstenen, Denmark's oldest stone

Mørupstenen is a so-called Larvikit, which is "horizontal" to Denmark during the penultimate ice age. Larvikit is a coarse-grained rock that is only found in southern Norway west of the Oslo Fjord. You are therefore called the larvikite for a leader block, as it can precisely lead us back to where the ice of its time came from. For more than 115,000 - 120,000 years, Mørupstenen has been on the field near Snejbjerg. Here it lies as an iceberg, where only part of the stone is visible. 8.6 meters long, 4.4 meters wide and 0.5 meters above the ground - but when you consider that the stone goes 3.5 meters underground and weighs just over 500 tonnes, then this is Denmark's second largest stone .

larvikit

Larvikite is a coarse-grained magma barge whose main constituent is labradorizing grain of alkali field splash. It builds up a large area around Larvik in the geological province of the Oslo field and is found in Denmark as a leader block or water residue. Almost 90 per cent of the larvikite consists of feldspar, and the crystals are composed in such a way that a blue color game appears when the light breaks in tiny lamellae internally within them. We call this optical phenomenon for the iridescence or Schiller effect. It is the very special composition of the field spat which is the reason for this. In addition to feldspar, larvikite contains small amounts of dark minerals, such as amphibole, olivine and biotite, and the most attractive varieties carry small amounts of the mineral nepheline. The larval surface is classified as monzonite in a QAP diagram, see below. A monzonite has approximately equal amounts of plagioclase and alkali feldspar and less than 5% quartz (light white glittering). Larvikit is used because of the beautiful color play as the facade stone and has gained wide spread. The rock is a variety of augitsyenit / monzonite, which is an important rock in many magma provinces, which can be seen in southern Greenland.

 

Hiking Block

A Hiking block (also called an erratic block; from Latin erratus: astray, ie geologically misplaced) is a (often very large) rock of a rock type, which is only found as a fixed mountain far from the stone's location, often several hundred km. Walking blocks have been led by the inland ice (during the ice age) and left when the ice melted (what is often, somewhat erroneously, called "when it retreated"). If the origin of the stone can be established, it can reveal which ice has passed along the way.

Denmark's largest walking block is Hesselagerstenen near Nyborg on Funen.

Here is the GC code for the earthcache

Task:

1 Study and observe the characteristics of Larvikit on the stone with the help of a flashlight.What happens?

1.1 Examine the size of the larval crystal grain and how large would you rate them to be?

2 At the coordinates you can see that there are cracks in the stone when an unknown farmer in the 1920s tried to break the stone into pieces. how many "small stones" can you count here?

3 Take a picture of yourself, or your GPS, on the stone. This is not a requirement for logging.

Send your discovery and an explanation to my profile email (Team Hvisthule)

Please first send the answers as the guidelines say, otherwise I will delete your log without comment. I'll get in touch if necessary With the answers there should be ambiguities.

Source indication: The information for the cache is mainly from VisitHerning, Wikipedia and Henning Sørensen: larvikit i Den Store Danske, Gyldendal. Hentet 17. marts 2019 fra http://denstoredanske.dk/index.php?sideId=114785