Framework/tectosillicates Flashcards
What are the main rock groups present within the framework/tectosillicate group?
Quartz, feldspar, feldspathoids, zeolites
What is the typical hardness of feldspar?
6/6.5
What type of twinning is common in feldspar minerals?
Perthite twinning where albite (a form of plagioclase) intergrows in fine lamella within k feldspar
Describe the cleavage of k and plagioclase feldspars
Two perfect/good cleavage directions supposed to intersect at near 90 degrees
Nepheline is an example feldspathoid. It commonly resembles quartz, but what three factors allow it to be distinguished?
- Hardness 5/6 when compared to quartz 7
- Greasy lustre when compared to quartz typical vitreous
- Has one cleavage plane- QUARTZ DOES NOT
What factor separates quartz from all other framework/tectosillicates?
NO CLEAVAGE
What are the three feldpathoids you need to identify?
Nepheline, sodalite, leucite
leucite appears similar to which zeolite? how can you distinguish the two?
analcime. honestly can seem to find valid ways to ditinguish between them
identify the follwing feldspathoid mineral:
Habit:
- football/hexagonal crystal shape when visible
hardness:
- 5/6 (scratched by qhartz glass)
lustre:
- typically vitreous
cleavage:
- one poorly formed direction might be visible
colour:
- typically white but could be others due to impurities
streak colour:
-white/non-visible
Leucite- the distinguishing thing will be the sorta ball shaped/hexagonal cleavage direction
Nepheline and quartz appear VERY similar to one another, how can you distinguish between the two?
nepheline is softer (hardness 5/6 vs 7) and has a poorly formed cleavage direction - quartz has conchoidal fracturing
state the key physical properties of sodalite
habit: - prismatic/isometric grains colour: - bright blue colour, but darker than that of lazurite streak colour: - typically no streak colour hardness: - 5/6 (scratched by quartz glass) lustre: - can range from vitrous to greasy
what are the key diagnostic properties that separate lazurite, nepheline and leucite from one another and other minerals? (these are all felsdpathoids)
sodalite:
- has a distinct blue colour, common vitreous lustre and hardness 5/6
Leucite:
the football shaped aggregates (in the lab sample you can see it clearly its a plain brow rock with white circular crystals in it). It also has one potwential cleavage direction
nepheline:
- the habit is different to leucite (commonly isometric) and has a cleave direction and hardness 5/6
what is the most common sodalite?
lazurite
name the key zeolites that we have specimines for and thus need to be able to identify
- Scolecite
- Mesolite
- Thomsonite
- Chazabite
- stillbite
- Heulandite
- Analcime
a zeolite has the following properties, identify it:
habit:
- isometric football/hexagonal shaped crystals
colour:
white. no streak
lustre:
- commonly vitreous
cleavage:
- has one really poor cleavage direction
hardness:
-3/4 (scratched by steel nail)
analcime
how can you distinguish anaclime from other zeolites?
its isometric/cubic/hexagonal crystal habit
what is the diangostic feature of stillbite and which group does it belong to?
a weird bow tie shaped crystal habit - belongs to the zeolite group
which zeolite can be idnetified from the following properties?: habit: - elongated/cubic - one good cleavage direction -hardness 3/4 vitreous lustre
heulandite
state the general physical properties of heulandite
habit: -elongated/cubic colour: white/pink lustre: -vitreous hardness: - 3/4 cleavage: one good cleavage direction
scoloectie and mesolite are BOTH zeolites with radial aggregation and acicular crystal habits. how can you tell the difference?
the crystals are so fibrous in mesolite that they cna at times not even be visible, and in the class specimines there is a defintie difference between the size- mesolite crystals ar ebigger (look back on the document)
which of the zeolites give acicular/fibrous crystals?
- scolecite
- mesolite
- Thomsonite
the physical properties describe which zeolite?: habit: acicular aggregation: radial colour: white, no streak hardness: 3/4 lustre: vitreous cleavage: one direction (between the crystals)
scolecite
the follwing properties describe which mineral? habit: - fibrous aggregation: - radial colour: - white/no streak Lustre: - vitreous hardness: 1-2 (scratched by finger nails) cleavage: one direction
mesolite
what are the diagnostic properties of mesolite and what group does it belong to?
- hardness is only 1/2 and the habits are very fibrous with radial aggregation
which zeolite can you indeitfy from the follwing properties? Habit: isometric- weird ball shaped aggregation but not similar to analcime colour: - white/pink hardness: - 3/4 cleavage: - one direction lustre: - vitreous
Stillbite
stae the physical properties of chazabite and which group it belongs to
habit: - cubic aggregation - granualr colour - white/ no streak lustre: -vitreous hardness: - 3/4 scratched by steel nail cleavage: - one very poor direction
how can you distinguish chazabite from other zeolites (considering they share A LOT of properties)
- it is the only zeolite sample with a very clear cubic habit (the rest have a isometric ball/hexagonal shaped habits)
which of the zeolite samples have a block/granular crystal shape?
chazabite and analcime
which of the zeolite samples has platy/tabular/isometric habits?
heulandite, Thomsonite, stillbite
