Earthcache requirements:
In order to log this earthcache you must answer the following questions. You do not have to wait for a reply before logging your find. I attempt to reply to all e-mails submitting answers and, if there are any problems I will contact you to obtain more information.
Task 1: Describe the overall colouring of the sandstone that you can see and why you think there is such a variety of colours.
Task 2: Describe the colour and types of iron oxides represented in the sandstone flagging.
Task 3: Do you see any banding on the sandstone flagging? Describe what you see and the type of iron oxide predominantly on display.
The answers to these questions should not be included in your log, nor should your log include spoiler photos. Please send the answers to me via message or e-mail.
Task 4: One last thing before you go...please go to the Waypoint "Photo Location - Stage 2" and take a photograph of yourself, your GPS, or a personal item showing the station building, including the [WINDSOR] sign and post this in your log.
Earth science lesson
For this earthcache, the posted coordinates will take you to the sandstone flagging directly in front of the historic station building.
Hawkesbury Sandstone
Hawkesbury Sandstone is primarily composed of quartz sandstone, with quartz grains making up a significant portion of the rock. These quartz grains are typically medium to coarse-grained and can be subangular to subrounded. The sandstone also contains minor amounts of other materials like shale, clay, and siderite.
Hawkesbury Sandstone exhibits a range of colors, primarily due to iron oxides and other minerals. These colors can vary from light yellow-brown to golden yellow, and even reddish-brown or orange. Some sandstone also displays banded patterns, where different minerals create a visually striking array of colors.
Common Minerals Found in Hawkesbury Sandstone:
- Quartz - Most abundant mineral (over 70%). Very hard and resistant, it gives the rock its strength and pale color. Appears as clear to milky white grains.
- Feldspar - Present in smaller amounts. Typically weathered and altered to clays (like kaolinite).
- Clay minerals (especially kaolinite) - From the weathering of feldspars. Adds to the fine matrix between quartz grains. Usuallay soft, white clay mineral.
- Iron oxides (especially hematite) - Often present as a pigment, giving reddish or yellowish hues to some layers.
- Micas (e.g., muscovite, biotite) - Present in trace amounts. Thin, shiny flakes are sometimes found between grains.
- Lithic fragments - Pieces of other rocks, usually volcanic or sedimentary, indicating the source rocks.
- Calcite (rare) - Sometimes present as cement, but not common—Hawkesbury is usually silica-cemented.
Iron Oxide Colouring in Hawkesbury Sandstone
Hematite (Fe₂O₃)
- Color: Red to reddish-brown
- Form: Thin coatings on quartz grains, pigment in the matrix, or small nodules
- Origin: Forms in well-oxygenated (oxidizing) conditions
- Effect: Responsible for the classic reddish tints and bands in some layers of Hawkesbury Sandstone
- Fun fact: Similar to the iron in rust and often used as a pigment (called "red ochre")
Goethite (FeO(OH))
- Color: Yellow-brown to ochre
- Form: Fine coatings or patches, often mixed with clays
- Origin: Forms in somewhat wetter conditions than hematite; can replace or form from other iron minerals
- Effect: Causes yellowish and brownish discoloration in parts of the rock
- Behavior: Less stable than hematite over time; may alter further with weathering
Magnetite (Fe₃O₄) (Rare)
- Color: Black
- Form: Trace mineral, occasionally as tiny grains
- Origin: Usually inherited from the original source rocks or volcanic fragments
- Effect: Not common enough to affect bulk color but may appear under a microscope
- Magnetic: Yes – helps identify it in lab settings
Limonite (Mixture, FeO(OH)·nH₂O)
- Color: Yellow-brown to dark brown
- Form: Amorphous or earthy coatings and masses
- Origin: Not a true mineral—it's a mixture that forms as iron oxides hydrate and alter
- Effect: Often present in weathered zones; contributes to earthy textures and colors
- Note: Common in weathered sandstone and soils
Banded Sandstone
"Banded" sandstone refers to the presence of contouring lines or veins in the stone. This banding is a characteristic feature of many types of sandstone, particularly those from the Hawkesbury Basin.
Layered Banding from River Deposits (Sedimentary Banding)
- This happens when sand was laid down by rivers in different layers over time.
- Some layers are coarser (with bigger grains), and others are finer (with smaller grains), depending on how fast the water was flowing.
- These layers can look wavy or slanted, kind of like ripples frozen in time.
Rusty-Looking Iron (Ferruginous) Banding
- These form when water moves through the rock and leaves behind iron, which then rusts.
- The bands are reddish, orange, or brown.
- They show that water has moved through the rock after it was formed.
Clay or Mica Banding
- Sometimes, tiny bits of clay or shiny minerals like mica settled in between the sand grains.
- These create thin, darker layers in the rock.
- They often show up when the river slowed down and allowed finer stuff to settle.
Hard, Light-Colored Bands (Limestone or Carbonate Banding)
- Occasionally, water with dissolved lime (like in limestone) moved through the rock and left behind hard white-ish bands.
- These are less common but stand out because they’re paler and tougher.
Wavy or Curved Iron Stains (Liesegang Banding)
- These are strange-looking curved or ring-like patterns, often reddish.
- They form much later, when water carrying iron moves through the rock and causes chemical reactions.
- They aren’t from the original layering but from changes after the rock formed.
References
About SideTracked Caches
This cache belongs to the SideTracked series. It is not designed to take you to a magical place with a breath taking view. It's a distraction for the weary traveller, but anyone else can go and find it too. More Information can be found at the SideTracked Website
Windsor Station
Opened on 1 December 1864, coinciding with the opening of the Richmond line. The original station building was a combination residence and office.
Original Windsor Railway Station 1864 to 1883, replaced in 1883.
The old building was re-erected as a house at 8 Mileham Street, Windsor
Image courtesy of Hawkesbury Library Service: Image No. 007292
A major upgrading of most stations on this line occurred in the 1880s, including Windsor. In April 1883 the contract for a brick station building and platform was awarded to G. Jones.
Windsor Railway Station (date unknown)
Image courtesy of Hawkesbury Library Service: Image No. 006443
The 1883 station building is a fine example of a Victorian second-class station building and is a significant landmark within the historic town centre. Windsor Railway Station was added to the New South Wales State Heritage Register on 2 April 1999. Today, Windsor Station is one of three stations incorporating larger station buildings built on the Richmond line during the 1880s. Today, train services are on the T1 Western and T5 Cumberland lines.
Did you know that NSW has a geocaching association? Geocaching NSW aims to enhance and improve the activity of geocaching and holds regular events where geocachers meet to enjoy their common interests. Visit the association website here.