By Sara Sjolin, MarketWatch

LONDON (MarketWatch) -- U.K.'s FTSE 100 index dropped for a sixth-straight week on Friday with RSA Insurance PLC tumbling after the chief executive resigned, while ARM Holdings PLC rallied on news Google may use its technology.

The benchmark index lost 0.1% to close at 6,439.96, ending the week 1.7% lower.

RSA Insurance Group slumped 7.2% after Chief Executive Simon Lee resigned and the company warned that its troubled Irish unit will hit 2013 earnings.

Oil firms further slipped as oil prices dropped and UBS cut the oil and gas sector to neutral from overweight. Royal Dutch Shell PLC (RDSB) dropped 1% and BP PLC (BP) lost 1.1%.

Centrica PLC gave up 0.6% after Société Générale cut the gas-utility firm to hold from buy.

On a more upbeat note, shares of ARM Holdings (ARMHY) jumped 3% after Bloomberg reported that Google Inc. (GOOG) is considering making its own server processors, using technology from the U.K. chip designer.

Among other stocks, shares of AstraZeneca PLC (AZN) rose 1.8% after the drug maker said an experimental gout drug met its goal in a late-stage clinical trial.

Most mining firms posted small gains after UBS lifted the sector to overweight from neutral. Randgold Resources Ltd. moved 1.8% higher, Glencore Xstrata PLC (GLCNF) slipped 0.3% and Fresnillo PLC added 0.2%.

Anglo American PLC , however, lost 0.4% after Deutsche Bank cut the miner to hold from buy.

Outside the main index in London, Thomas Cook Group PLC slid 3.2% after Nomura cut the travel operator to reduce from neutral. The analysts expressed concerns about the management's margin targets and said the recent outperformance was due to headlines and "low-hanging fruit."

More from MarketWatch:

Markets up, but retirements still at risk

Rich bet on 'sane' subprime

Investor bullishness looks 'horrifying'

Subscribe to WSJ: http://online.wsj.com?mod=djnwires

Glencore (PK) (USOTC:GLNCY)
Gráfico Histórico do Ativo
De Jul 2024 até Ago 2024 Click aqui para mais gráficos Glencore (PK).
Glencore (PK) (USOTC:GLNCY)
Gráfico Histórico do Ativo
De Ago 2023 até Ago 2024 Click aqui para mais gráficos Glencore (PK).