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Both zinc ore Sphalerite and calcium plagioclase feldspar Anorthite have perfect cleavage that will split cleanly if you hit them with a hammer, but only one can claim a larger split of your votes!
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Illite from
Castle Nook Mine, Newlands Valley, Above Derwent, Allerdale, Cumbria, England, UK


Locality type:Mine
Classification
Species:Muscovite var: Illite
Formula:K0.65Al2.0[Al0.65Si3.35O10](OH)2
Age information
Maximum recorded age:395 Ma
Minimum recorded age:362 Ma
Sample ages:
Recorded ageGeologic TimeSampleDating method
1381 MaLate/Upper Devonian - K-Ar
2369 MaLate/Upper Devonian - K-Ar
3362 MaLate/Upper Devonian - K-Ar
4395 MaEarly/Lower Devonian - K-Ar
Sample references:
1 -
Ineson, P. R., Mitchell, J. G. (1974) K-Ar isotopic age determinations from some Lake District mineral localities. Geological Magazine, 111 (6). 521-537 doi:10.1017/s0016756800041571
2 -
Ineson, P. R., Mitchell, J. G. (1974) K-Ar isotopic age determinations from some Lake District mineral localities. Geological Magazine, 111 (6). 521-537 doi:10.1017/s0016756800041571
3 -
Ineson, P. R., Mitchell, J. G. (1974) K-Ar isotopic age determinations from some Lake District mineral localities. Geological Magazine, 111 (6). 521-537 doi:10.1017/s0016756800041571
4 -
Ineson, P. R., Mitchell, J. G. (1974) K-Ar isotopic age determinations from some Lake District mineral localities. Geological Magazine, 111 (6). 521-537 doi:10.1017/s0016756800041571
Confirmation
Validity:Believed Valid
Data
Mineral Data:Click here to view Illite data
Locality Data:Click here to view Castle Nook Mine, Newlands Valley, Above Derwent, Allerdale, Cumbria, England, UK
Data Identifiers
Mindat Occurrence Record ID:16535
Long-form Identifier:1:3:16535:2
GUID (UUID V4):0
Nearest other occurrences of Illite
1.5km (0.9 miles) ⓘGoldscope Mine, Newlands Valley, Above Derwent, Allerdale, Cumbria, England, UK
2.7km (1.7 miles) ⓘYewthwaite Mine, Newlands Valley, Above Derwent, Allerdale, Cumbria, England, UK
4.6km (2.9 miles) ⓘWad Mine, Seathwaite, Borrowdale, Allerdale, Cumbria, England, UK
5.3km (3.3 miles) ⓘForce Crag Mine, Coledale, Above Derwent, Allerdale, Cumbria, England, UK
8.8km (5.5 miles) ⓘThornthwaite Mine, Thornthwaite, Above Derwent, Allerdale, Cumbria, England, UK
12.2km (7.6 miles) ⓘBrundholme Mine (Glenderaterra Mine; Blencathra Mine), Glenderaterra Valley, Threlkeld, Eden, Cumbria, England, UK
13.3km (8.3 miles) ⓘThrelkeld Mine, Threlkeld, Threlkeld, Eden, Cumbria, England, UK
13.7km (8.5 miles) ⓘGreenside Mine, Patterdale, Eden, Cumbria, England, UK
18.6km (11.6 miles) ⓘCarrock Mine, Mungrisdale, Eden, Cumbria, England, UK
18.9km (11.8 miles) ⓘRoughton Gill, Caldbeck, Allerdale, Cumbria, England, UK
References
Day, Harry (1999) BMS Database, British Micromount Society.
 
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