Geology 101 : Scoria
(This cache is the sister cache of GC90P0R to help differentiate between Basalt and Scoria.)
So you have found yourself in the Alice Wylie Reserve instead of whizzing past it!
It was declared a reserve in 1980, and formally taken over by the Mt Albert City Council in 1982, the year the council named it after Alice Wylie, then a sitting member of the council.
Near to you is a statue. The "Statue of a Cloaked Woman" was placed in 1994 to commemorate the woman of Mount Albert past and present. It was vandalized in 2022 and replaced in a new position in 2024. Originally, the statue sat on a mound of scoria, representing the significant volcanic history of the area.
The mount is now about 4-5 meters away from the statue under some trees. There is a photo in the gallery with the mount circled in relation to the statue.
The park has a few more interpretive signs and some nice shady benches to sit on.
Warning:
Do not try to drive into the driveway, it's gated and closed for cars.
Earthcache Logistics:
The area is easily reached by bike, by foot, or by public transit.
Parking can be found on the side streets, please pay attention to any postage signage.
This cache should only take you a few minutes, but if you have more time, stay awhile and enjoy the park.
You will probably need to leave the path to answers the questions.
You will need to visit the posted coordinated and answer a few questions.
This Earthcache should not be done at night.
This cache can be fun for all ages.
There are a couple of information signs in the park, if you are interested they are worth the read!
Mostly, HAVE FUN!!!
---So, let's get to the GEOLOGY.---
The word scoria comes from the Greek “skoria”= rust.
Scoria is a dark-colored extremely vesicular basaltic lava with very small (< 1mm) abundant round bubble-like cavities called vesicles.
Scoria is classified as an extrusive igneous rock.
Scoria forms when magma containing huge amount of dissolved gas bubbles out from a volcano during an eruption. Sort of like.a soda can releasing carbon dioxide when it is opened.
Most scoria is basaltic or andesitic in composition.
Also referred to as scoriaceous basalt, which is commonly used to indicate a basaltic pumice. It is commonly composed of approximately 50% silica and 10% calcium oxide with lesser contents of potash and soda.
Major mineral components are plagioclase, pyroxene and olivine. Minor mineral contents may include apatite, biotite. hematite, hornblende, ilmenite, magnetite and quartz.
Scoria usually has a composition similar to basalt, but it can also have a composition similar to andesite.
Scoria has a relatively low density as a result of its numerous macroscopic ellipsoidal vesicles. But still have a specific gravity greater than 1 and sinks in water. (Compared to pumice that may float on water).
Scoria has a bubbly appearance, which differentiates it from the more solid and uniform appearance of a basalt lava flow.
Scoria is a fine grained, opaque durable rock with a medium hardness (5-6).
It typically has a vesicular texture. Color can vary, black, brown, dark grey to red are all common.
Scoria is gathered around the vents of a volcano. The cone-shaped hills formed by Scoria is called an ash cones. Auckland has many of these Scoria cones spread around the city, for example Maungarei / Mount Wellington and the quarry cones at Te Tatua-a-Riukiuta / Three Kings.
Scoria is often used for landscaping and drainage (for example of retaining walls). It is commonly used to make roads in New Zealand and also can be used for traction on icy and snowy roads. Mount Wellington, Big King and Mt. Roskill are all reservoirs.
It has commercial use as a high-temperature insulating material. For example, a gas BBQ may have scoria rocks near the flames.
How to identify Scoria:
Color : Black or dark gray to deep reddish or purpleish brown. (due to composition differences pumice is almost always white to light gray to light tan.)
Texture : Typically has abundant very small (< 1mm) round bubble-like cavities known as vesicles. (The vesicles in pumice contain enough air that the rock will float on water. The thick walls of scoria make it heavy enough to sink.)
In scoria that is weathered, it becomes more difficult to see the vesicles.
How to log this Earthcache:
(Answered to be sent to my geocaching account, photos can be posted with the log.)
A) Near to the posted coordinates is a bronze statue.
Q1) Please take a photo of yourself, your GPS, your caching name on a piece of paper, or even your shoe with the statue in view.
(Photo required for logging, so I know you visited the park).
(See example photo in gallery)
Update - 14 Feb. 2023: The photo is absoluetly REQUIRED to be attached to the log, no exceptions. Do not send the photo to the CO, post it in the log. This photo only need to be proof you visited. It can be as simple as your caching name on a piece of paper. Thank you!
B) Examine the rocks of the mound that the statue sits on.
Q2) Describe the nature of these stones (texture, color, etc).
Q3) Why are you certain that these rocks are Scoria? How was this rock formed? (Compared to pumice or basalt, for example).
COPY / PASTE QUESTIONS :
For your convenience, you can copy / paste the questions to answer from here:
Required questions for logging -
Q1) Please take a photo of yourself, your GPS, your caching name on a piece of paper, or even your shoe with the statue in view.
Q2) Describe the nature of these stones (texture, color, etc).
Q3) Why are you certain that these rocks are Scoria? How was this rock formed? (Compared to pumice or basalt, for example).
Need help?
Are you confused on a question? Don't stress! I'm looking for answers that showed me you went to the site and tried.
If there are any problems I will contact you and I am happy to help further or add some information.
If you have any further questions, please feel free to send me a message, read the information boards or look at the following references.
Logging:
Feel free to log this Earthcache immediately.
However, after 10 days, any log that is not accompanied by a message with the answers and a photo will be unceremoniously deleted.
Update - 14 Feb. 2023: The photo is absoluetly REQUIRED to be attached to the log, no exceptions. Do not send the photo to the CO, post it in the log. This photo only need to be proof you visited. It can be as simple as your caching name on a piece of paper. Thank you!
References:
https://en.wikipedia.org/wiki/Scoria
Geology Science. (2020). Scoria. [online] Available at: https://geologyscience.com/rocks/scoria/