The posted coordinates brings you to the Masjid Jamek Pedestrian Bridge, over the River of Life. The bridge is cladded with a type of limestone called travertine, and in it you can see various fossils as highlighted in GC89972. With closer inspection of the bridge, you will notice the the colouration throughout is not the same. And if you look carefully, the way the crystals appear in these dark spots are very different. 

Calcite

Calcite is a carbonate mineral and the most stable polymorph of calcium carbonate (CaCO₃). The Mohs scale of mineral hardness, based on scratch hardness comparison, defines value 3 as "calcite".

Over 800 forms of calcite crystals have been identified. Most common are scalenohedra, with faces in the hexagonal {2 1 1} directions (morphological unit cell) or {2 1 4} directions (structural unit cell); and rhombohedral, with faces in the {1 0 1} or {1 0 4} directions (the most common cleavage plane). Habits include acute to obtuse rhombohedra, tabular forms, prisms, or various scalenohedra. Calcite exhibits several twinning types adding to the variety of observed forms. It may occur as fibrous, granular, lamellar, or compact. A fibrous, efflorescent form is known as lublinite.Cleavage is usually in three directions parallel to the rhombohedron form. Its fracture is conchoidal, but difficult to obtain.

Scalenohedral faces are chiral and come in pairs with mirror-image symmetry; their growth can be influenced by interaction with chiral biomolecules such as L- and D-amino acids. Rhombohedral faces are achiral.

In geology, calcite is a common mineral formed in limestone and marble.

Crystal Habits

In mineralogy, crystal habit is the characteristic external shape of an individual crystal or crystal group. A single crystal's habit is a description of its general shape and its crystallographic forms, plus how well developed each form is.

Recognizing the habit may help in identifying a mineral. When the faces are well-developed due to uncrowded growth a crystal is called euhedral, one with partially developed faces is subhedral, and one with undeveloped crystal faces is called anhedral. The long axis of a euhedral quartz crystal typically has a six-sided prismatic habit with parallel opposite faces. Aggregates can be formed of individual crystals with euhedral to anhedral grains. The arrangement of crystals within the aggregate can be characteristic of certain minerals. For example, minerals used for asbestos insulation often grow in a fibrous habit, a mass of very fine fibers.

The following are a few of the many crystal habits.

1. Acicular - appears as needles
2. Banded - appears as layers of different colors/minerals
3. Bladed - appears as blades of knives
4. Botryoidal - appears as a bunch of circles. Resembles grapes maybe?
5. Cubic - appearas as a cube
6. Dendritic - appears as leaf veins/tree branches
7. Massive - shapeless, no distinctive external crystal shape
8. Radiating - protruding outwards from a center point
9. Stalactitic - appears as stalactites or stalagmites

Logging Tasks

Any part of the bridge can be used to answer the questions. However, the image below points out the best spot to look for the answers. Send the answers via my profile and log a find. I will get back to you if there are any doubts about your answers.

1. The bridge here is made from travertine, a form of limestone which is calcite. There are some darker patches around the bridge. Are these still calcite?
2. Why do you think there are darker patches?
3. Take note of these darker patches and tell me what crystal habit(s) you can see.
4. The lighter patches also exhibit some crystal habits. What can you see?
5. Optional: Post a photo proving you have visited the site.