Skip to content

Sydney Opera House Rocks - Feldspar EarthCache

Hidden : 4/27/2017
Difficulty:
1.5 out of 5
Terrain:
1.5 out of 5

Size: Size:   other (other)

Join now to view geocache location details. It's free!

Watch

How Geocaching Works

Please note Use of geocaching.com services is subject to the terms and conditions in our disclaimer.

Geocache Description:

In this eartch cache we are going to be paying a closer attention not only to the beautifull shells of the Sydney Opera House, but also to the materials of the platform where the are resting. In Utzon's designs both parts had the same importance, so let's go and check them out!.


Architectural Marvel

From the outset, Danish architect Jørn Utzon had a vision to create a striking sculptural form, one that would relate naturally to the undulating waves of Sydney’s superb harbour. Organic materials and colours therefore form the fundamental elements of Utzon’s design: a strong red-granite base anchors the arched white sails that soar elegantly into Sydney’s skyline. 

Sydney Opera House’s Forecourt is one of the world's most spectacular outdoor performance spaces and offers the largest capacity of any Opera House venue. Set below the famous white sails and the granite Monumental Steps, the Forecourt offers patrons harbour and city views. 

International icons such as Florence and the Machine, Björk, Oprah, The National, Crowded House, Sting and The Wiggles have all performed here to thousands of adoring fans. Queen Elisabeth II oficially inaugurated the building from this forecourt on October 1973.

Apart from the tile of the shells and the glass curtain walls of the foyer spaces, the building's exterior is largely clad with aggregate panels composed of pink granite quarried at Tarana in the central west of New South Wales. 



GEOLOGY OF THE ROCKS AT THE SYDNEY OPERA HOUSE

1. Granite

Granite is a plutonic igneous rock formed by the slow cooling of a magma (molten aluminum) to great depths of the earth's crust. This prolonged cooling allows large crystals to form, giving rise to the characteristic crystalline texture of the granites.

They consist of three essential minerals: quartz (transparent, white, gray ...) feldspar (white, pink, red, yellow, brown, green and gray), mica and a very variable group of accessory minerals, presented in percentages Less than 5%, such as apatite, sphene, oxides, allanite, zircon, amphiboles, etc. (black color).

Granite  is  one  of  the  most  valuable  stones  for  construction  purposes.  Although  the  quality  of  granite  varies  according  to  the  proportions  of  the  constituents  and  to  their  method  of  aggregation,  this  kind  of  stone  is  generally  durable,  strong,  and  hard.  The  hardest  and  most  durable  granites  contain  a  greater  proportion  of  quartz  and  a  smaller  proportion  of  feldspar  and  mica.  Feldspar  makes  granite  more  susceptible  to  decomposition  by  the  solution  potash  contained  in  it,  potash  feldspar  being  less  durable  than  lime  or  soda  feldspar.  Mica,  being  easily  decomposed,  is  an  element  of  weakness  in  granite.  An  excess  of  lime  or  soda  in  the  mica  or  feldspar  hastens  disintegration,  as  does  also  an  excess  of  iron.  Therefore,  stones  showing  large  and  dark  iron  stains  should  be  rejected  for  outside  work.  Fine-grained granite weathers better than does granite of coarser grain.

Granite has a pearly lustre.  The  colour  of  common  granite  varies  from  white  through  yellow  to  deep  red,  and  the  stone  is  generally  classified  as  gray  and  red.  Feldspar renders the stone lighter in colour.

Because  of  its  uniform  structure,  granite  can  be  quarried  in  large  blocks.  The  rift,  the  grain,  and  the  joint  planes  are  advantageous  in  quarrying,  as  it  is  very  difficult  to  cut  granite  in  other  places.  The  uses  for  which  granite  is  suitable  depend  on  the  texture  of  the  stone.  Medium-grained stone is best fitted for building construction.  Fine-grained  stone  can  be  carved  and  polished,  but,  on  account  of  its  extreme  hardness,  it  cannot  be  worked  readily.  Such  stone  is,  therefore,  costly  when  it  has  to  be  cut,  Coarse-grained  granite  should  be  used  only  for  concrete  aggregate.

2. Feldspar

Feldspars are a group of mineral roofs and aluminosilicates corresponding in volume to as much as 60% of the earth's crust. The composition of feldspar constituents of rocks corresponds to a ternary system composed of orthoclase (KAlSi3O8), albite (NaAlSi3O8) and anorthite (CaAl2Si2O8).

Feldspars with a chemical composition between anorthite and albite are called plagioclase, while feldspars with a composition between albite and orthoclase are called feldspars potassic. Feldspar is an essential component of many igneous, sedimentary and metamorphic rocks such that many of these rocks are classified according to their feldspar content. The feldspar structure can be described as a shell of silicon and aluminum with alkali bases and alkaline earth metals in the void spaces.

Granite is the hardest stone that humans use for construction. The hardness of a stone or mineral is measured using the Mohs scale. Granite has a measure of seven out of 10 on the Mohs scale. It also has a dense grain content. This makes it stain-resistant and wear-resistant, and gives it high load-bearing capacity. Granite is almost completely devoid of porosity and does not readily absorb water.

Quartz has a hardness of 7 on the Mohs scale, feldspar 6, and mica is always less than 6 but the hardness of granite varies according to the quarry.

There are two simple rules for assessing the quality of granite:

1.- Grain size: In general terms, the larger the grain of the granite, the lower its hardness and the greater its ease of crumbling.

2.- Color: the darker the granite, it is that it has less quartz ratio, therefore, the less hard it is. On the contrary, the clear granites, having more proportion of the harder material in their composition will be harder as well.


1+2 = Alkali feldspar granite

Alkali feldspar granite, some varieties of which are called 'red granite', is a felsic igneous rock and a type of granite rich in the mineral potassium feldspar (K-spar). It is a dense rock with a phaneritic texture. The abundance of K-spar gives the rock a predominant pink to reddish hue; peppered with minor amounts of black minerals.

As shown in the QAPF diagram, alkali feldspar granite contains between 20% - 60% quartz. Less quartz content would lead to "quartz alkali feldspar syenite". More than 90% of the total feldspar content is in the form of alkali feldspar. Less than that amount would designate the rock as a granite.

Other incorporated silicate minerals may include, very minor amounts of plagioclase feldspar, mica in the form of muscovite and/or biotite, and amphibole (often hornblende). Oxide minerals such as magnetite, ilmenite, or ulvospinel. Some sulfides and phosphates (mainly apatite) may also be present.



To log this Earthcache as found it you should:

 

 Send us an e-mail with the answers to the following questions:

-What colors can be seen in the feldspars in the granite of the Opera House Forecourt? What is the percentage of this feldspars in the granite? Taking in mind your answers and with the above information, what type of granite is the one used at the Sydney Opera House forecourt?>

-What other colors/materials can also be seen in the granite?

Estimate the grain size of the granite: A- < 1mm; B- 2-4 mm or C- > 6mm.

- With the data above How do you think the granite quality of the Opera House Forecourt is? Why?.

 Walk inside the Opera House Building Main Ticket Office foyer and visit one of the four restrooms on that level. Inside you will find on the walls the same granite but polish. What differences can you appreciate on the granite blocks compare to the ones outside?

 [Optional] Take a photo of the place with you GPS in it.

Logs with answers included will be deleted.

Additional Hints (No hints available.)